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. 2022 Dec 14;17(12):e0278337. doi: 10.1371/journal.pone.0278337

Public support for global vaccine sharing in the COVID-19 pandemic: Evidence from Germany

Ferdinand Geissler 1,*, Felix Hartmann 1, Macartan Humphreys 2,3, Heike Klüver 1, Johannes Giesecke 1
Editor: Sara Rubinelli4
PMCID: PMC9750013  PMID: 36516143

Abstract

By September 2021 an estimated 32% of the global population was fully vaccinated for COVID-19 but the global distribution of vaccines was extremely unequal, with 72% or more vaccinated in the ten countries with the highest vaccination rates and less than 2% in the ten countries with the lowest vaccination rates. Given that governments need to secure public support for investments in global vaccine sharing, it is important to understand the levels and drivers of public support for international vaccine solidarity. Using a factorial experiment administered to more than 10,000 online survey respondents in Germany in 2021, we demonstrate that the majority of German citizens are against global inequalities in vaccine distribution. Respondents are supportive of substantive funding amounts, on the order of the most generous contributions provided to date, though still below amounts that are likely needed for a successful global campaign. Public preferences appear largely to be driven by intrinsic concern for the welfare of global populations though are in part explained by material considerations—particularly risks of continued health threats from a failure to vaccinate globally. Strategic considerations are of more limited importance in shaping public opinion; in particular we see no evidence for free riding on contributions by other states. Finally, drawing on an additional survey experiment, we show that there is scope to use information campaigns highlighting international health externalities to augment public support for global campaigns.

Introduction

Vaccination is the key to overcome the COVID-19 pandemic. Multiple vaccines have been developed in record time and more than 12 billion doses administered and 63% of the global population fully vaccinated by October 2022. Already by September 2021 an estimated 32% of the global population was fully vaccinated. However, the global distribution of the COVID vaccines has been extremely unequal [1]: By that time about 72% of citizens were vaccinated in the ten countries leading in the COVID vaccination campaign, less than 2% of the population is vaccinated in the ten most poorly performing countries. Those top 10 and bottom 10 countries are from among 102 countries with populations >500, 000 that report vaccination rates. Strikingly, based on calculations on data by [1], per capita GDP alone explains as much as 56% of this variation in vaccination rates; COVID mortality about 8% (calculations available in replication materials).

Besides the evident inequities, and the economic and health threats to poorer countries [2], the unequal provision of vaccines has important consequences for wealthier countries and the international order [35]. The risks from low global provision include economic and health threats arising from continued interruptions of global supply chains, and the preservation of reservoirs that facilitate emergence of SARS-CoV-2 variants/mutations. One study estimates global costs at €9 trillion [6]. It has been estimated that approximately 70% of the worldwide population must be fully vaccinated to end the COVID-19 pandemic [7]. The delta variant has pushed the threshold for global herd immunity to 80% and potentially approaching 90% [8]. The rise of the Omicron variant cannot be stopped with the vaccines that are currently available, but at least the spread can be slowed down and morbidity and mortality associated with the disease can be reduced. Thus, vaccine inequity is not only a humanitarian disaster, it is one that has direct material consequences for wealthier countries.

Researchers at the International Monetary Fund (IMF) estimate the costs of global vaccination at $50 billion [6]. Other estimates put costs closer to €80 billion. Though there is no clear determination of what a fair share is, as a benchmark, if the richest 25% of countries provided €70 per citizen this would sum to 80 billion Euros and imply contributions of about €6 billion for Germany and €23 billion for the United States. Using the Fair Share calculation, based on OECD guidelines, Germany’s share of OECD donor shares would be €5bn (8% of €63bn) (for details see [9]). Given its size and wealth this is about four times the average corresponding contribution of other wealthy nations.

However, a fair distribution of COVID-19 vaccines is not only a matter of providing money, as vaccines continue to be scarce for some time. Despite the importance of globally distributing COVID-19 vaccines to stop the pandemic, most Western countries have launched campaigns for a third shot and a number of countries even started the distribution of a fourth vaccination (e.g. Israel, USA, Chile, Denmark or Germany) in the wake of the Omicron wave [10]. Poorer countries will therefore continue to struggle to obtain sufficient vaccines for their citizens in the foreseeable future. On 4 August 2021, WHO director Tedros Adhanom Ghebreyesus therefore called for a moratorium halting COVID-19 vaccine boosters in favor of unvaccinated (see Reuters).

Given that governments need to secure public support either for making large monetary contributions or for sharing vaccines with poorer countries, it is important to understand the levels and drivers of public support for global vaccine sharing and to identify ways through which governments can increase solidarity with other countries in need. Previous research has focused on ethical questions of global vaccine distribution [11, 12] or on mapping the international distribution of COVID-19 vaccines [13, 14]. However, little is known about public opinion on global vaccine sharing. In this study we focus on three motivations: intrinsic motivations, material motivations, and strategic motivations. By intrinsic motivations we refer to the preferences for sharing that derive from concerns for the well-being of global populations. By material incentives we refer to the economic and health benefits to German citizens that might arise from a global response. By strategic incentives, we refer to considerations that make the preferred German contribution dependent on what other states are providing to global vaccine sharing. We hereby build on related literatures on contributions to global public goods. In particular, past work on European solidarity during the Eurozone crisis [1518] and preferences for international climate agreements [19, 20], highlights how popular preferences are not only affected by both the specific costs and benefits for the donor country, but also by the design of multilateral agreements and the behavior of other countries. Building on this work we examine both the role of (stipulated) direct costs to Germany and the structure of international cooperation. We also assess the extent to which public support can be increased through information campaigns appealing to the self-interest of citizens.

Materials and methods

Our study draws on survey data and data from two survey experiments that we fielded in a multi-wave panel study in Germany using the online access panel of the survey company Respondi. Respondi relies on online channels and offline channels to recruit new panelists for its online panel. After completing a profiling questionnaire covering basic sociodemographic information, panelists are then invited to participate in surveys. Respondi compensates its panelists for completing a survey.

Our target population consists of all German citizens aged 18 to 75 years. In wave 1, the sample corresponded to the official national statistics with respect to age, sex and region, though the quality of this correspondence weakened somewhat by wave 4 (for details, see Table 1 and Section A in the S3 File). We conducted the experiments in wave 2 and 4 of the panel. All analyses were specified in preregistered analysis plans and the study obtained IRB approval at Humboldt-Universität zu Berlin (HU-KSBF-EK 2021 0019). Data and replication material are publicly available at https://wzb-ipi.github.io/vaccine_solidarity/.

Table 1. Sociodemographic characteristics.

Federal Statistical Office Wave 1 Wave 2 Wave 4 (panel) Wave 4 (refreshment)
Age
 18–29 0.18 0.19 0.14 0.10 0.18
 30–39 0.18 0.17 0.16 0.15 0.17
 40–49 0.16 0.18 0.18 0.19 0.18
 50–59 0.22 0.22 0.24 0.26 0.23
 60–75 0.26 0.24 0.28 0.30 0.25
Sex
 Female 0.50 0.50 0.48 0.44 0.50
 Male 0.50 0.50 0.52 0.56 0.49
 Other 0.00 0.00 0.00 0.00 0.00
Region
 Baden-Württemberg 0.13 0.13 0.13 0.12 0.13
 Bavaria 0.16 0.16 0.16 0.16 0.16
 Berlin 0.04 0.04 0.05 0.05 0.04
 Brandenburg 0.03 0.03 0.03 0.03 0.03
 Bremen 0.01 0.01 0.01 0.01 0.01
 Hamburg 0.02 0.02 0.02 0.02 0.02
 Hesse 0.08 0.08 0.08 0.07 0.07
 Mecklenburg-Vorpommern 0.02 0.02 0.02 0.02 0.02
 Lower Saxony 0.10 0.10 0.10 0.10 0.10
 North Rhine-Westphalia 0.22 0.22 0.22 0.22 0.22
 Rhineland-Palatinate 0.05 0.05 0.05 0.05 0.05
 Saarland 0.01 0.01 0.01 0.01 0.01
 Saxony 0.05 0.05 0.05 0.05 0.05
 Saxony-Anhalt 0.03 0.03 0.03 0.03 0.03
 Schleswig-Holstein 0.03 0.03 0.03 0.03 0.03
 Thuringia 0.03 0.03 0.03 0.03 0.03

Experiment 1

The first experiment draws on data generated from a factorial online survey experiment that was implemented in wave 4 of the panel study which was administered to 10,525 respondents between 8 and 22 September 2021. In the experiment, participants first received an introductory text explaining the need for global vaccine sharing to overcome the pandemic. Afterwards, respondents were asked to consider a hypothetical scenario which randomly varied along four dimensions (health benefits, economic benefits, number of countries participating, contribution of other countries). Respondents were then asked to indicate how much Germany should contribute to global vaccine sharing, both in € and in vaccine doses. Each respondent received two vignettes successively.

More specifically, two dimensions focused on the benefits of global vaccine sharing for Germany in terms of public health and in terms of economic growth. One asked participants to imagine that “The risk of new mutations of the coronavirus increases considerably in Germany if there are no vaccinations in poorer countries”; a second asked participants to imagine that “The German economy shrinks by around 5% if there are no vaccinations in poorer countries.” For each of these a control condition was provided in which there were no costs to Germany if there are no vaccinations in poorer countries (see Table 2).

Table 2. Experimental design: Factors and levels.

Factor Level
Trade (0) No negative impact on German economy if no vaccinations in poorer countries
(1) German economy shrinks by 5% if no vaccinations in poorer countries
Risk (0) Risk of new mutations does not increase if no vaccinations in poorer countries
(1) Risk of new mutations increases if no vaccinations in poorer countries
Deal (0) No international deal on the distribution of vaccines to poorer countries.
(1) International deal: 20 other countries, total 20 billion euros
(2) International deal: 40 other countries, total 20 billion euros
(3) International deal: 20 other countries, total 40 billion euros
(4) International deal: 40 other countries, total 40 billion euros

The other two dimensions focused on the nature of multilateral agreements, asking participants to imagine settings in which 0, 20 or 40 countries took part, contributing collectively €0, €20, or €40 billion. In all there are five types of agreement considered (because 0 participants implies 0 contributions and vice versa). In all this gives rise to a 2 × 2 × 5 factorial design (see complete wording of the factor levels in the appendix).

Experiment 2

The second survey experiment was conducted in wave 2 of the panel study which was fielded between 29 April and 10 May 2021 (see Section D in the S3 File for further information). In this experiment, participants were randomly assigned to a treatment group that is exposed to a video explaining the benefits of global vaccine sharing and a control group which did not see the video. The video emphasizes in particular the risk of more mutations forming if vaccines are not made available in developing countries. Subsequently, respondents were asked whether they support the international distribution of vaccines (attitudinal outcome) and were offered the opportunity to donate money to UNICEF which was put in charge for global vaccine sharing (behavioural outcome). More specifically, respondents earned 75 so-called “Mingle Points” cents in token appreciation for their participation in the survey (this corresponds to 0.75 Euros). We offered them 50 additional Mingle Points and gave them the following choice. They could either keep the 50 Mingle Points for themselves or donate all or part of them to UNICEF for the worldwide distribution of Corona vaccines. For every point they donated, we donated 1.5 Euro Mingle points to UNICEF (see Table 4 in the S3 File).

We only present results for the personal donation outcome since the conjoint had a flawed design. For full transparency we present results of the conjoint experiment in the S3 File.

Survey data on beneficiary prioritization

To measure humanitarian motivations directly, we included a question in both waves 2 and 4 asking respondents to indicate how the German government should prioritize to ensure vaccination for an older Indian woman as compared to a younger German woman in the second and fourth wave of the panel study.

Analytic approach

We implement two types of analysis.

The first type of analysis using regression analysis to compare groups across conditions. For the primary analysis we estimate the effects of treatment conditions on two outcomes, Cashcontributions (in billion Euros), and Doses (millions). Estimates are generated by regressing outcomes on four conditions (Amount given by other countries, Number of others giving, Risk, Trading importance) along with all interactions and allowing for individual level fixed effects.

Yij=β0+β1X1+β2X2+β3X3+β4X4+β5X1X2+β6X1X3+β7X1X4+β8X2X3+β9X2X4+β10X3X4+β11X1X2X3+β12X1X2X4+β13X1X3X4+β14X2X3X4+νi+ϵij

All conditions (X1X4) are centered on zero which allows us to read average effects directly from main terms (β1β4) [21]. Estimates are generated together with robust standard errors using the estimatr::lm_robust function in R [22].

We use the same analytic procedure when analyzing the effects of the video treatment from Experiment 2 though here there is only one treatment and one response per respondent and there are no interaction terms or fixed effects included in the analysis.

A second type of analysis estimates parameters from a structural model. For this analysis we assume that individuals evaluate own country (yi) and other country ((yj)) contributions according to the objective function:

u=(α+β×economicrisk+δ×healthrisk)×log(-iyj+yi)-γ×(yi-κy¯)2-yi2

where y¯ is the average contribution of other states, and ∑i jj is the total contributions by others. We note that this expression differs from the expression in our pre-analysis plan in not subscripting parameters by respondent. This model builds on standard models of a multiplayer public goods production problem (see e.g. [23]). The basic form is bgc where g is the public good produced, b is marginal benefits and c is the cost of contributions. We allow marginal benefits to depend on the type of public good specified by treatment variations (health risks and economic risks). We also assume diminishing returns to the public good and convex costs. We depart from classic models by allowing for the possibility of peer effects—that subjects seek to benchmark their contributions to those of others (see e.g. [24]). Together γ and κ capture how much (γ) and how (κ) individuals might seek to match Germany’s contributions to those of others, whether they value Germany giving more (κ > 1), less κ < 1 or the same (κ = 1) as the average contribution of other countries.

Letting yi* denote optimal own contributions given economic and health risks and the contributions of others, we assume that players report yi*+ϵi where ϵiN(0, σ2) captures deviations from predictions of the model.

We estimate parameters (α, β, δ, γ, κ, σ) using maximum likelihood implemented via bbmle::mle2 in R.

Finally our analysis of beneficiary prioritization uses simple means in respondents answers.

Results

Experiment 1

Fig 1 graphs raw data patterns to show the share of Germans supporting contributions of €X or less (top panel) or X donations of vaccine doses (bottom panel) or less. We indicate, separately, preferred contributions when there are high costs meaning that there are large economic and health costs of the status quo for Germany (versus low costs meaning there are no economic and health costs) and a situation of high multilateralism meaning that there is a major international deal (versus low multilateralism meaning there is no international deal).

Fig 1. Distribution of support for contributions of different sizes.

Fig 1

We see that median favored contributions are around €2 bn and 100 million doses, an amount closely in line with actual current German commitments. There is considerable heterogeneity, however, with about one third support commitments around €5 bn or more. A small share—around 1 in 8, support much larger contributions. Given the skewed nature of the distributions, the average amount proposed is much larger—around €8 bn Euros for cash, but the mean number of doses proposed is lower at around 80 million.

In Figs 6–9 in Section E of the S3 File we document variation in these levels of support across subgroups. Based on preregistered analyses we show first, that support varies substantially as a function of political party support— with the greatest support among Green party voters and voters of the social democratic SPD whereas support is weakest among voters of the right-wing populist AfD. Second we show variation as a function of migration background, with substantially greater support for higher levels of solidarity among respondents with a migration background. We note nevertheless that despite this variation, support is high in all groups. To wit, a majority of AfD supporters, the group least likely to support international vaccine solidarity, still support contributions of 1 billion Euros or more.

In Fig 1 we can also see that both sets of conditions increase the size of contribution supported by survey participants. These differences are generally statistically significant (see below) but as seen from the raw data, the effects are quantitatively small.

Fig 2 shows the marginal effects of all conditions on optimal cash donations and vaccine doses. This represents the same underlying patterns as seen in Fig 1 though the focus here is on average effects. Overall we see that both health risks and trading importance are statistically distinguishable from zero. While this effect may be small compared to Germany’s overall budget, it is a sizable effect when using the median donations as a benchmark.

Fig 2. Marginal effects of conditions.

Fig 2

Strikingly the amounts offered are positively responsive to amounts given by other countries, but unresponsive to the number of other countries giving. This is the opposite to what one might expect from accounts that focus on free-riding between states understood as the failure to contribute a fair share to global vaccine distribution if other states already donate large amounts. Our results instead suggest a willingness to support initiatives regardless of average contributions by other countries.

Our heterogeneity analysis (in appendix) suggest that these treatment effects are quite similar for respondents that support different parties or that have different migration backgrounds.

Our preregistered structural estimation lets us shed more light on the intrinsic, material, and strategic motivations of respondents. The estimated structural parameters from this analysis are given in Table 3.

Table 3. Structural parameter estimates.

parameter estimate std.error statistic p.value conf.low conf.high
α 240.62 2.01 119.73 0.00 236.68 244.56
β -10.32 12.71 -0.81 0.42 -35.23 14.59
δ 37.79 12.45 3.04 0.00 13.40 62.19
γ 0.61 0.07 9.22 0.00 0.48 0.75
κ 5.22 0.40 13.06 0.00 4.44 6.00
σ 15.98 0.08 205.18 0.00 15.83 16.14

We see here strong evidence for marginal gains from contributions independent of economic and health risks (α), these marginal gains are increased (δ) when there are substantial health risks (by about 16%), but are not much affected by economic risks (β). Respondents place weight on alignment with other countries (γ), but the results on κ suggest that they target contributions that are significantly higher (five times higher) than the average amount given by other nations. Note that average contributions by other countries was not provided directly to respondents, though it can be calculated from the numbers and the amounts given. The implied factor of 5 is remarkably close—and somewhat higher—than the factor of 4 that we calculated using the fair share calculation.

Experiment 2

Consistent with the findings presented above we found evidence for quite high baseline willingness to contribute in experiment 2 implemented in the second wave of the panel study. The median contribution is 40% and the most common response—chosen by about a third of respondents—was to contribute the full amount of this funding to UNICEF. Fig 3 reports the results of the information experiment. We find that respondents in the treatment group that were exposed to the video are significantly more likely to show solidarity both with regard to the attitudinal and the behavioral outcome. More specifically, the reported willingness to personally support international distribution of vaccines is 0.069 units higher than in the control group. In a similar vein, the average actual donations that respondents made to UNICEF were significantly higher in the treatment than in the control group. The average effect of treatment is a 4 percentage point increase in amounts offered.

Fig 3. Effect of video treatment on individual solidarity.

Fig 3

Priorities analysis

Turning to the analysis of prioritization, we find that 57% of the respondents place the priority of the older Indian woman as high or higher than the German woman, and 38% even place it strictly higher.

Discussion

Our results show that German citizens are supportive of generous contributions to the global distribution of vaccines against COVID-19. Median popular support is somewhat below estimated contributions needed to fund global vaccine redistribution; though average amounts exceed this. Popular preferences for global vaccine solidarity appear to primarily stem from humanitarian concerns and are only in part explained by material and strategic considerations. While there is a preference for multilateral efforts, public support for large contributions to global vaccine distribution does not depend on the behavior of other countries. We furthermore show that information campaigns can increase public support for international vaccine solidarity.

We interpret the high rates of solidarity in the control conditions—when there are no health or economic benefits stipulated—as evidence of non-strategic humanitarian concerns. Our analysis of support priorities supports this interpretation. The comparison we examined there directly pitted nationalist concerns against humanitarian concerns. We would expect any strategic considerations that enter in the decision to prioritize an Indian woman should apply a fortiori to the prioritization of a German woman.

Overall these results support the conclusions that German citizens see intrinsic benefits from global contributions, that these are augmented, but do not depend on externalities—health externalities in particular—and that Germans, insofar as they benchmark contributions to those of other nations, do not support free riding and indeed value contributing at rates higher than those of other wealthy nations. Our results moreover show that there is not only a high baseline willingness to contribute to global vaccine sharing, but that the solidarity expressed by citizens can be significantly increased by providing information about the benefits of global vaccine distribution.

Before concluding, we discuss a set of plausible threats to validity. The first relates to a set of critique in [25] that highlights difficulties that respondents have in providing numeric valuations of public goods. Focusing on contingent valuation surveys in economics, [25] highlight risks that respondents may not have well defined valuations of public goods, may not be in a position to take relevant budget constraints into account (which can lead to what is sometimes called an embedding effect), and provide answers that cannot easily be assessed against revealed preferences. Although our experiment bears similarities with contingency valuation surveys our aim here is not to assess individual willingness to pay for global vaccinations, but rather to assess what policies respondents would like to see public officials follow. Their report of these preferences to us, which in turn get communicated publicly, albeit in aggregated form, bears a direct relation to the policy quantities of interest which is absent for contingency valuation surveys; by the same token, embedding effects may indeed be real in the formulation of policy priorities. However, this does not imply a bias in measurement, but rather a threat of inconsistencies in policy demands.

Although the aim of our study is different to those of scholars assessing the valuation of public goods, we still recognize that survey responses may not accurately predict the policy preferences that would advocate in a policy context when the benefits and costs of different strategies are debated by political actors, and responses may be sensitive to question wording, for instance, or the information we supplied to contextualize costs. Fully addressing these questions would require implementing a field analogue of our study, perhaps involving discussions between politicians and citizens [26].

Our findings have clear implications for the current debate on international vaccine solidarity in the COVID pandemic. With regard to the instruments of achieving a fair allocation of vaccines globally, the evidence presented in Figs 1 and 2 shows that patterns of support for monetary and dose donations are similar. However, the value of median preferred dosage donations (90 million doses) is substantively smaller than the median preferred cash donations (2 billion) if we assume the costs per vaccine to be around 6 Euro per dose [6]. This is in part an artifact of the fact that dosage donations by Germany are capped by vaccine holdings; nevertheless it highlights the fact that framing sharing in terms of vaccines rather than cash, by suggesting a zero sum nature of the problem, may yield weaker support for sharing. There are, however, many other avenues to address vaccine inequality including strategies that target production in developing countries, through financing, extending intellectual property rights, and sharing know-how.

We acknowledge that this study only uses stated preferences for hypothetical scenarios so that it remains unclear whether the effect sizes would be the same under similar real world scenarios. However, it has been shown that stated preferences are indeed predictive of actual behavior [27]. We only use data from an online survey in Germany and rely on an access panel. For future research it would be beneficial to use different modes and multiple other countries as well.

Conclusions

Our study has shown that the stark inequalities in global vaccine distribution are not in line with public opinion. Vaccine nationalism, though evident in policy, is a minority position in Germany. The results of our study have important implications for the current public debate on global vaccine distribution, but also for international solidarity and international cooperation more generally. On the one hand, the COVID-19 vaccination is a highly salient issue for all citizens worldwide and thus provides a unique opportunity to study popular preferences for international solidarity. On the other hand, since herd immunity is a global public good as the pandemic can only be overcome if all countries worldwide are immunized, our findings can furthermore inform the literature on preferences for international cooperation.

Our study also has important implications for the debate on international solidarity [1518] and global public goods [19, 20] more generally. We show that public support for international solidarity in global vaccine sharing is positively affected by the amounts given by other countries which corroborates the findings from previous research on global climate cooperation and EU bailouts [15, 19]. However, there is no evidence for free-riding as citizen support is not conditional on the number of other countries participating in global vaccine sharing, in contrast to findings on public attitudes towards global climate agreements [19]. Finally, our study adds to the current debate by showing public support for international solidarity is malleable and that informing citizens about the benefits of vaccine sharing could increase support.

While efforts to share vaccines globally have been a failure to date, the evidence we provide importantly suggests that this is not due to lack of public support for the proposition. Average proposals exceed current contributions by the German government and also exceed fair share calculations of what the German government ought to be providing. Median proposals are somewhat less than the fair share benchmark, but nevertheless large. Evidence from our experiment with ancillary data suggest that strategic considerations matter, but are not paramount in explaining public preferences. Rather humanitarian rationales loom large. In all, these results suggest that policy-makers who take up the mantel of addressing the challenge of achieving global vaccination will have the moral support of the public behind them.

Supporting information

S1 File

(PDF)

S2 File

(PDF)

S3 File

(PDF)

Data Availability

Data and replication material is available at https://wzb-ipi.github.io/vaccine_solidarity/.

Funding Statement

Research for this contribution is part of the Cluster of Excellence "Contestations of the Liberal Script" (EXC 2055, Project-ID: 390715649; https://www.scripts-berlin.eu/), funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany´s Excellence Strategy. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Decision Letter 0

Sara Rubinelli

20 Jun 2022

PONE-D-22-09640Public support for global vaccine sharing in the COVID-19 pandemic: Intrinsic, material, and strategic driversPLOS ONE

Dear Dr. Geissler,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Both reviewers are pleased with the overall framework of the paper. They, however, suggested important revisions that need to be carefully addressed before further considering this manuscript for publication. 

Please submit your revised manuscript by Aug 04 2022 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

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If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Sara Rubinelli

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: I Don't Know

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: No

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The manuscript by Geissler et al. is interesting, relevant, and timely. However, the structure/organization of the manuscript is confusing (Results described in the Introduction, Methods described in the Results, Discussion of findings in Results, etc.). Moreover, several key pieces of information about the sample, procedures, and analytical approach are not described, limiting this manuscript’s public health contributions.

Specific comments go below:

• Title

Include location and time frame of the study in the Title.

• Abstract

What does top/bottom 10 mean? Largest economies? Human development index?

“we show that global inequities are out of line with domestic German public opinion.” Is editorialized. Please reframe.

“we see no evidence for free riding on contributions by other states.” Please explain further.

• Intro

First paragraph needs citations.

Please describe “strategic motivations” and how they differ from “intrinsic motivations” in greater detail.

The authors present findings and their implications in the Introduction, which is confusing. The 2 last paragraphs in the Introduction should be moved to the Results and Discussion, respectively.

• Methods

While the factorial experiment procedures are described in detail, more information on recruitment activities, inclusion/exclusion criteria, and analysis methods are needed in this section. For example: was this a nationally representative sample? Who was eligible to participate?

The first paragraph of the Structural analysis should be moved to the Methods.

More information on how the authors arrived at their structural model should be provided.

• Results

What are main sociodemographic characteristics of the sample? How do they map onto Germany’s national demographics?

In Figure 1, how did you define high vs. low costs and multilateralism?

What are thresholds for considering effect sizes small vs. large? A difference of over 1 billion Euros in investment and 50 million doses between high vs. low risk do not seem “not large”

In Figure 2, what does the treatment effect of “amount given by others” mean? For each 10 billion more Euros other countries invest, participants believed Germany should invest about 0.25 billion more?

Please provide further explanation on the meaning of parameters gamma, sigma, and kappa in your structural function.

Please provide your working definition of “free riding”.

The last paragraph of the Results should be discussed in the Discussion.

• Discussion

It is very hard to follow the second and third paragraphs of the Discussion. It is unclear how the second paragraph of the Discussion relates to this paper. Please explain. Were the experiments discussed in the second and third paragraphs of the Discussion conducted as part of the present study or were they separate?

It seems that new findings are presented in the second and third paragraphs of the Discussion. These should be moved to the Results section.

The last paragraphs of the discussion should also discuss Limitations in the sampling approach (was this a nationally representative sample? How were participants recruited? Phone interviews? Online? Etc.)

• Conclusion

The first paragraph of the Conclusion should be moved to the Discussion. How are the authors comparing monetary vs. vaccine contributions?

“Finally, our study adds to the current debate by showing that governments could increase support for international solidarity through information campaigns.” This point is overstated. It is not clear if treatment effects seen in your experiment would be reproduced in mass information campaigns.

Reviewer #2: 1.Title

OK

2.Abstract

The statement ……over 85 % vaccinated in the top 10 countries and below 3 % in the bottom 10. It is not clear who are top ten and bottom ten, what is the basis of classification is it GDP? World Bank ranking? Poverty index. It should be stated clear

3.Background/Introduction

• There are multiple currency being used in the paper USD$ and Euro € para. 3 page 2…. the costs of global vaccination at $50 billion… Since the text is predominantly reported in Euro, this should translated to the same currency

• The background aims at establishing the main question that the paper is trying to answer and link it with previous research in the field, and why it is important. The paper largely has managed to provide that. However, on. Pg. 2… the last paragraph …Our results show that German citizens are supportive of generous contributions to the global distribution of vaccines against COVID-19. Median popular support is somewhat below estimated contributions…. From this paragraph to the end of the introduction section the authors start presenting results, which is contrary to the aim of this section, this paragraphs will serve better by being moved into results, discussion and conclusion sections.

4.Methods

OK

5.Results

OK

6.Discussion

OK

7.Conclusion and Recommendation(s) Most of the text in para 1 and 2 pg. 6 on conclusion section, while providing valid information, the authors continue discussing the results instead of drawing a conclusion. It is important that authors ONLY conclude the study results and implications based on results and discussion. No need to use reference in this section, rather conclude the study.

8.References

OK

9.Figures

Need to improve the quality of the figures

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: Yes: George M Ruhago

**********

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While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2022 Dec 14;17(12):e0278337. doi: 10.1371/journal.pone.0278337.r002

Author response to Decision Letter 0


4 Aug 2022

Dear Reviewers,

Thank you very much for the thoughtful reviews of our manuscript.

We have endeavored to address all of your concerns and suggestions. We have thoroughly revised the manuscript on the basis of the reviewer and editor comments.

Below, we explain in detail the modifications we have made. Editor and reviewer comments are written in italics; our responses follow in normal font. To indicate changes that we have conducted in the manuscript, we highlight all changes in the main text in red.

________________________________________

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

________________________________________

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: I Don't Know

Reviewer #2: Yes

________________________________________

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

● All our data is publicly available at https://wzb-ipi.github.io/vaccine_solidarity/. We have mentioned this before only in the first footnote, but we are now making this much more explicit by directly stating the availability of the data and replication materials in the main text of the research design section.

________________________________________

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: No

● We carefully revised the entire paper to make sure that there are no typographical or grammatical errors.

________________________________________

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The manuscript by Geissler et al. is interesting, relevant, and timely. However, the structure/organization of the manuscript is confusing (Results described in the Introduction, Methods described in the Results, Discussion of findings in Results, etc.). Moreover, several key pieces of information about the sample, procedures, and analytical approach are not described, limiting this manuscript’s public health contributions.

Specific comments go below:

• Title

Include location and time frame of the study in the Title.

● We changed the title to “Public support for global vaccine sharing in the COVID-19 pandemic: Evidence from Germany” and clearly added the time frame to the abstract and the Methods discussion.

• Abstract

What does top/bottom 10 mean? Largest economies? Human development index?

● We changed the sentence as follows:

As of September 2021 an estimated 27% of the global population was fully vaccinated for COVID-19 but the global distribution of vaccines was extremely unequal, with 70% or more vaccinated in the ten countries with the highest vaccination rates and less than 1% in ten countries with the lowest vaccination rates.(FOOTNOTE Numbers calculated from figures from Our World in Data for countries with reported vaccinations and with populations of at least 500,000. See replication materials)

“we show that global inequities are out of line with domestic German public opinion.” Is editorialized. Please reframe.

● We have reframed the sentence as follows:

“We demonstrate that the majority of German citizens are against global inequalities in vaccine distribution.”

“we see no evidence for free riding on contributions by other states.” Please explain further.

● We have reformulated the sentence as follows:

“in particular we see no evidence for free riding on contributions by other states as the level of preferred donations are positively responsive to the contributions of other countries.”

• Intro

First paragraph needs citations.

● We have added a citation to Mathieu at al. (2021) on which basis we have calculated the reported numbers. The paragraph now reads as follows:

“Vaccination is the key to overcome the COVID-19 pandemic. Multiple vaccines have been developed in record time and more than 9 billion doses have been administered globally to date. As of early 2022 an estimated 50% of the global population is fully vaccinated. However, the global distribution of the COVID vaccines is extremely unequal (Mathieu et al. 2021): Fewer than 1% of doses administered have been administered in low income countries. While about 85% of citizens are vaccinated in the ten countries leading in the COVID vaccination campaign, less than 3% of the population is vaccinated in the ten least performing countries. Strikingly, per capita GDP alone explains as much as 60% of the variation in vaccination rates; COVID mortality about 6%

“The numbers are calculated from data from Our World in Data; calculations available in replication materials.”(Footnote: Numbers calculated based on data provided by Mathieu et al. (2021); calculations available in replication materials.)

Please describe “strategic motivations” and how they differ from “intrinsic motivations” in greater detail.

● To address this point, we have rewritten the text passage in question as follows:

“By strategic incentives, we refer to considerations that make the preferred German contribution dependent on what other states are providing to global vaccine sharing. We hereby build on related literatures on contributions to global public goods. In particular, past work on European solidarity during the Eurozone crisis (Bechtel, Hainmueller and Margalit, 2017; Kuhn, Nicoli and Vandenbroucke, 2020; Kuhn, Solaz and van Elsas, 2018; Stoeckel and Kuhn, 2018) and preferences for international climate agreements (Bechtel, Genovese and Scheve, 2019; Bechtel and Scheve, 2013), highlights how popular preferences are not only affected by both the specific costs and benefits for the donor country, but also by the design of multilateral agreements and the behaviour of other countries. Building on this work we examine both the role of (stipulated) direct costs to Germany and the structure of international cooperation.”

The authors present findings and their implications in the Introduction, which is confusing. The 2 last paragraphs in the Introduction should be moved to the Results and Discussion, respectively.

● Following the suggestions of the reviewer, we have moved the last two paragraphs to the Results and Discussion sections.

• Methods

While the factorial experiment procedures are described in detail, more information on recruitment activities, inclusion/exclusion criteria, and analysis methods are needed in this section. For example: was this a nationally representative sample? Who was eligible to participate?

● In order to address this comment, we have added a new Section in the Supplementary Material (Section A) and have carefully revised the methods section and extended the text passages in question as follows:

“Our study draws on two survey experiments that we fielded in a multi-wave panel study in Germany. At the start of the panel, the sample was nationally representative according to age, sex and region (for details, see the supplementary materials). We conducted the experiments in wave 2 and 4 of the panel. In order to conduct the factorial survey experiment, we fielded the experiment relying on the online access panel of the survey company Respondi. Respondi relies on online channels and offline channels to recruit new panelists for its online panel. After completing a proling questionnaire covering basic sociodemographic information, panelists are then invited to participate in surveys. Respondi compensates its panelists for completing a survey. Our population of interest consists of all German citizens aged 18 to 75 years.”

The first paragraph of the Structural analysis should be moved to the Methods.

● We thank the reviewer for this suggestion. Having carefully examined the paper again, we worried that this material would be important for readers to understand the analysis. Instead of moving this part we have tried to make this whole discussion more readable.

More information on how the authors arrived at their structural model should be provided.

We have added the following motivation to the text:

● “This model builds on standard models of a multiplayer public goods production problem (see e.g. Hellwig (2013)). The basic form is bg - c where g is the public good produced, b is marginal benefits and c is the cost of contributions. We allow marginal benefits to depend on the type of public good specified by treatment variations. We also assume diminishing returns to the public good and convex costs. We depart from classic models by allowing for the possibility of peer effects — that subjects seek to benchmark their contributions to those of others (see e.g. Fischbacher and Gächter (2010).”

replacing the previous overly brief account:

“The function assumes diminishing marginal returns to total contributions, convex costs of own contributions, substitutability of own and other contributions for global benefits, and a possible desire to benchmark contributions against the contributions of others.”

• Results

What are main sociodemographic characteristics of the sample? How do they map onto Germany’s national demographics?

● We added a new table with sociodemographic characteristics comparing official data with the distribution in the different waves in the Supplementary Material (Table 3). We have also added a new Section in the Supplementary Material (Section B) to show which impact panel attrition has on the results of Experiment 1.

In Figure 1, how did you define high vs. low costs and multilateralism?

● We did two things to make it easier to understand these terms. First, we added Table 1 to show the factors and levels of the experimental design. Second, we reformulated the text passage as follows:

“We indicate, separately, preferred contributions when there are high costs meaning that there are large economic and health costs of the status quo for Germany (versus low costs meaning there are no economic and health costs) and a situation of high multilateralism meaning that there is a major international deal (versus low multilateralism meaning there is no international deal).”

What are thresholds for considering effect sizes small vs. large? A difference of over 1 billion Euros in investment and 50 million doses between high vs. low risk do not seem “not large”

● We have reformulated the sentence to give a benchmark for the effect sizes.

“Overall we see that both health risks and trading importance are statistically distinguishable from zero, but, as seen already, the magnitude of effects is not large considering that the federal budget of Germany for 2021 was around € 500 bn.”

In Figure 2, what does the treatment effect of “amount given by others” mean? For each 10 billion more Euros other countries invest, participants believed Germany should invest about 0.25 billion more?

● Yes, the interpretation is correct. In order to make it clearer to the readers, we changed the label in Figure 2 from “amount given by others” to “amount given by other countries”.

Please provide further explanation on the meaning of parameters gamma, sigma, and kappa in your structural function.

● gamma: gamma captures the weight that players place on the extent to which their contributions are in line with those of other states

● kappa:kappa captures the extent to which players, if they benchmark their contributions to those of others, seek to match (kappa = 1), exceed (kappa >1) or provide less than (kappa <1) others

● sigma: captures the variance of an error term that allows for deviation from the predictions of the mode; if the model explains behavior very tightly, sigma will be small;

We now provide more explanation for these terms in the text.

Please provide your working definition of “free riding”.

● We have added the following discussion to the main text:

“This is the opposite to what one might expect from accounts that focus on free-riding between states understood as the failure to contribute a fair share to global vaccine distribution if other states already donate large amounts. Our results instead suggest a willingness to support initiatives regardless of average contributions by other countries.”

The last paragraph of the Results should be discussed in the Discussion.

● As suggested we moved the last paragraph of the Results Section to the Discussion Section.

• Discussion

It is very hard to follow the second and third paragraphs of the Discussion. It is unclear how the second paragraph of the Discussion relates to this paper. Please explain. Were the experiments discussed in the second and third paragraphs of the Discussion conducted as part of the present study or were they separate? It seems that new findings are presented in the second and third paragraphs of the Discussion. These should be moved to the Results section.

● We agree that it was somewhat confusing how we presented the results of our two experiments in the original version of the manuscript. In order to address this point, we have therefore carefully revised the entire methods, results and discussion section to explain in detail that we conducted two different survey experiments as part of wave 2 and wave 4 of our panel survey in Germany.

The last paragraphs of the discussion should also discuss Limitations in the sampling approach (was this a nationally representative sample? How were participants recruited? Phone interviews? Online? Etc.)

● As suggested above, we have explained in much more detail how the sample is constructed and how respondents were recruited in the Materials and Methods. We also added a paragraph on limitations at the end of the Discussion Section.

“We acknowledge that this study only uses stated preferences for hypothetical scenarios so that it remains unclear whether the effect sizes would be the same under similar real world scenarios. However, it has been shown that stated preferences are indeed predictive of actual behavior (Hainmueller, Hangartner and Yamamoto, 2015). Moreover, we only use data from an online survey in Germany and rely on participants of an access panel. For future research it would be beneficial to use different modes and multiple other countries as well.”

• Conclusion

The first paragraph of the Conclusion should be moved to the Discussion.

● As suggested, we have moved the paragraph to the Discussion Section.

How are the authors comparing monetary vs. vaccine contributions?

● Because the scales of the two different measures are distinct we do not directly compare the treatment effects. When comparing the median of the preferred dosage donation and the preferred cash donation, we now explain that we follow the estimated costs per dosage by Agarwal and Gopinath (2021). We therefore reframed the conclusion as follows:

“However, the value of median preferred dosage donations (90 million doses) is substantively smaller than the median preferred cash donations (2 billion) if we assume the costs per vaccine to be around 6 Euro per dose (Agarwal and Gopinath, 2021).”

“Finally, our study adds to the current debate by showing that governments could increase support for international solidarity through information campaigns.” This point is overstated. It is not clear if treatment effects seen in your experiment would be reproduced in mass information campaigns.

● We have reframed the sentence as follows:

“Finally, our study adds to the current debate by showing public support for international solidarity is malleable and that informing citizens about the benefits of vaccine sharing could increase support.”

Reviewer #2:

________________________________________

1.Title

OK

2.Abstract

The statement ……over 85 % vaccinated in the top 10 countries and below 3 % in the bottom 10. It is not clear who are top ten and bottom ten, what is the basis of classification is it GDP? World Bank ranking? Poverty index. It should be stated clear

● We changed the sentence as follows:

“As of early 2022 an estimated 50% of the global population is fully vaccinated for COVID-19 but the global distribution of vaccines is extremely unequal, over 85% vaccinated in the top 10 countries and below 3% in the 10 countries with the lowest vaccination rate”

3.Background/Introduction

• There are multiple currency being used in the paper USD$ and Euro € para. 3 page 2…. the costs of global vaccination at $50 billion… Since the text is predominantly reported in Euro, this should translated to the same currency

● We have converged all US-Dollar indications to Euros.

• The background aims at establishing the main question that the paper is trying to answer and link it with previous research in the field, and why it is important. The paper largely has managed to provide that. However, on. Pg. 2… the last paragraph …Our results show that German citizens are supportive of generous contributions to the global distribution of vaccines against COVID-19. Median popular support is somewhat below estimated contributions…. From this paragraph to the end of the introduction section the authors start presenting results, which is contrary to the aim of this section, this paragraphs will serve better by being moved into results, discussion and conclusion sections.

● In order to address this point, we have moved the paragraph in question to the Discussion Section.

4.Methods

OK

5.Results

OK

6.Discussion

OK

7.Conclusion and Recommendation(s) Most of the text in para 1 and 2 pg. 6 on conclusion section, while providing valid information, the authors continue discussing the results instead of drawing a conclusion. It is important that authors ONLY conclude the study results and implications based on results and discussion. No need to use reference in this section, rather conclude the study.

● In order to address this point, we have moved all discussions of results to the Discussion Section and only discuss broader implications in the Conclusion.

8.References

OK

9.Figures

Need to improve the quality of the figures

● This seems to be an issue with the manuscript where the figures are presented in reduced quality. All figures were uploaded to PLOS One in high quality and can be downloaded using the links in the appendix of the manuscript (e.g., Figure 1: https://www.editorialmanager.com/pone/download.aspx?id=30923249&guid=28f0b479-470b-4b23-a0c1-e710710dd939&scheme=1).

Decision Letter 1

Sara Rubinelli

24 Aug 2022

PONE-D-22-09640R1Public support for global vaccine sharing in the COVID-19 pandemic: Evidence from GermanyPLOS ONE

Dear Dr. Geissler,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Both reviewers are pleased with the revision. Yet, one reviewers still has minor comments that I kindly ask you to address before I can make a final decision. 

Please submit your revised manuscript by Oct 08 2022 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

  • A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

  • An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Sara Rubinelli

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

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Reviewer #1: Yes

Reviewer #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #1: Yes

Reviewer #2: Yes

**********

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Reviewer #1: Yes

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors have been largely responsive to my initial comments. A few minor comments remain:

1- Abstract:

* Information in the abstract does not match the Introduction; please update the abstract (50% of the global population is vaccinated, etc., 85% vaccination in top 10 countries, etc.).

2- Introduction:

* Factual data needs citation (number of doses administered globally, etc.).

* I suggest you change "disease mutation" to "emergence of SARS-CoV-2 variants/mutations".

* Vaccines are not highly effective in preventing transmission of Omicron variants, but they still prevent morbidity and mortality associated with the disease. This should be noted in the 2nd paragraph.

* Several countries have recommended a fourth dose for some populations, not only Israel (US, Brazil, etc.). Please update.

3- Methods

* I believe there is a confusion regarding the meaning of "nationally representative sample". Having the same proportion of men/women, or the same age distribution of the general population does not necessarily mean that the sample is nationally representative. Representativeness of the sample is more about the sampling strategy and if everyone in the target population could have been in the study. Is that the case in this study? Is this a random sample of the German population? Is this a systematic sampling approach?

* Data access: I could not access the data file through the weblink provided, only the code used in analyses. Perhaps I am missing something obvious here, but I suspect other readers may also have trouble accessing the data used in this report.

* If possible, move Supplemental Table A to the main text, as we know that many readers do not access suppl materials.

*There should be a section in the Methods that describes the analytical approach employed.

4- Results

* I still think that the specification of the models should be discussed/explained in the Methods.

* I disagree that effect sizes are small. Take, for example, the effect of risk, which leads to a billion euro increase in donations (50% of the median contribution). This may be small compared to Germany's overall budget, but it seems like a substantial effect using the median donations as a benchmark. The responsiveness to health risks is also aligned with the significant effect of the educational video in increasing donations in Experiment 2.

* It is unclear to me why authors used the dichotomous outcome (donate all to UNICEF vs. not) rather than the continuous amount of Mingle Points donated. Please clarify.

5- Discussion

* The authors continue to present new findings in the Discussion. These should be moved to the Results (and included in the Methods) or excluded from this report.

Page 6: "we furthermore included a question asking respondents to indicate how the German government should prioritize to ensure vaccination for an older Indian woman as compared to a younger German woman in the second and fourth wave of the panel study.The comparison directly pits nationalist concerns against humanitarian concerns. Importantly also, we expect, any strategic considerations that enter in the decision to prioritize an Indian woman should apply a fortiori to the prioritization of a German woman. Strikingly, we nd that 57% of the respondents place the priority of the older Indian woman as high or higher than the German woman, and 38% even place it strictly higher."

* Were participants made aware of the cost of vaccines? The mismatch between money vs. vaccine contributions may be due to participants not knowing the average cost of vaccine doses.

Reviewer #2: (No Response)

**********

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Reviewer #1: No

Reviewer #2: Yes: GEORGE MUGAMBAGE RUHAGO

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PLoS One. 2022 Dec 14;17(12):e0278337. doi: 10.1371/journal.pone.0278337.r004

Author response to Decision Letter 1


12 Oct 2022

Reviewer #1: The authors have been largely responsive to my initial comments. A few minor comments remain:

1- Abstract:

* Information in the abstract does not match the Introduction; please update the abstract (50% of the global population is vaccinated, etc., 85% vaccination in top 10 countries, etc.).

• We thank the reviewer for pointing to this inconsistency. We have updated all numbers to match the timing of the survey. Though this is not the most recent data it is the most relevant for interpreting results and avoids working with a moving target.

2- Introduction:

* Factual data needs citation (number of doses administered globally, etc.).

• Thank you. We write now in a footnote:

“Numbers calculated based on data provided by Mathieu (2021); calculations available in replication materials. Top 10 and bottom 10 countries are from among 102 countries with populations > 500,000 that report vaccination rates.”

• We also now more clearly indicate the relevant section of the replication file (it is now labeled “3. Numbers provided in Introduction (Vaccine background data from OWID)”) and all calculations are implemented more transparently with consistent dates.

* I suggest you change "disease mutation" to "emergence of SARS-CoV-2 variants/mutations".

• We agree that this is more accurate and have changed it accordingly.

* Vaccines are not highly effective in preventing transmission of Omicron variants, but they still prevent morbidity and mortality associated with the disease. This should be noted in the 2nd paragraph.

• We reformulated the sentence as follows to capture this as well:

“The rise of the Omicron variant cannot be stopped with the vaccines that are currently available, but at least the spread can be slowed down and morbidity and mortality associated with the disease can be reduced..”

* Several countries have recommended a fourth dose for some populations, not only Israel (US, Brazil, etc.). Please update.

• That is correct. In the meantime more countries followed with this recommendation. We have adjusted this in the text.

“Despite the importance of globally distributing COVID-19 vaccines to stop the pandemic, most Western countries have launched campaigns for a third shot and a number of countries even started the distribution of a fourth vaccination (e.g. Israel, USA, Chile, Denmark or Germany) in the wake of the Omicron wave (Mahase, 2021).”

3- Methods

* I believe there is a confusion regarding the meaning of "nationally representative sample". Having the same proportion of men/women, or the same age distribution of the general population does not necessarily mean that the sample is nationally representative. Representativeness of the sample is more about the sampling strategy and if everyone in the target population could have been in the study. Is that the case in this study? Is this a random sample of the German population? Is this a systematic sampling approach?

• We agree with the reviewer. We have reformulated this part making it even more clear that the sample is not a "nationally representative sample", though we also detail how on available observable characteristics of the sample match the population. We also reformulated the paragraph in the Supplementary Materials A. accordingly

“Our study draws on two survey experiments that we fielded in a multi-wave panel study in Germany using the online access panel of the survey company Respondi. Respondi relies on online channels and offline channels to recruit new panelists for its online panel. After completing a profiling questionnaire covering basic sociodemographic information, panelists are then invited to participate in surveys. Respondi compensates its panelists for completing a survey.

Our target population consists of all German citizens aged 18 to 75 years. In wave 1, the sample corresponded closely to the official national statistics with respect to age, sex and region though the quality of this correspondence weakened somewhat by wave 4 (for details, see Table 1 and Section A in the Supplementary Materials). We conducted the experiments in wave 2 and 4 of the panel. All analyses were specified in preregistered analysis plans and the study obtained IRB approval at [Redacted Institution]. Data and replication material are publicly available at https://wzb-ipi.github.io/vaccine_solidarity/”.

* Data access: I could not access the data file through the weblink provided, only the code used in analyses. Perhaps I am missing something obvious here, but I suspect other readers may also have trouble accessing the data used in this report.

• The data will be made available under the provided weblink as soon as the paper gets published.

• We have edited the replication code however so that it runs from the cleaned data which we have made available already. As of now the reviewer should be able to replicate all analyses from the github replication archive.

* If possible, move Supplemental Table A to the main text, as we know that many readers do not access suppl materials.

• Following this suggestion, we moved the Table into the main text.

*There should be a section in the Methods that describes the analytical approach employed.

• We have adopted this suggestion and added a new section on analytic procedures/

4- Results

* I still think that the specification of the models should be discussed/explained in the Methods.

• We have adopted this suggestion and added a new section on analytic procedures/

* I disagree that effect sizes are small. Take, for example, the effect of risk, which leads to a billion euro increase in donations (50% of the median contribution). This may be small compared to Germany's overall budget, but it seems like a substantial effect using the median donations as a benchmark. The responsiveness to health risks is also aligned with the significant effect of the educational video in increasing donations in Experiment 2.

• We agree that the size of the effects could be evaluated differently depending on the benchmark. Therefore we reformulated the sentence.

“Overall we see that both health risks and trading importance are statistically distinguishable from zero. While this effect may be small compared to Germany's overall budget, it is a sizable effect when using the median donations as a benchmark.

* It is unclear to me why authors used the dichotomous outcome (donate all to UNICEF vs. not) rather than the continuous amount of Mingle Points donated. Please clarify.

• We do not use the dichotomous outcome in the analysis, we use the full data. In fact much of the data is in the all or nothing categories (see replication material section 8). This note on the differences in the highest category was intended to provide intuition for the movement behind the estimate which largely reflects this increase in the highest category. We have removed this point however to avoid confusion and simply note the average effect.

5- Discussion

* The authors continue to present new findings in the Discussion. These should be moved to the Results (and included in the Methods) or excluded from this report.

Page 6: "we furthermore included a question asking respondents to indicate how the German government should prioritize to ensure vaccination for an older Indian woman as compared to a younger German woman in the second and fourth wave of the panel study.The comparison directly pits nationalist concerns against humanitarian concerns. Importantly also, we expect, any strategic considerations that enter in the decision to prioritize an Indian woman should apply a fortiori to the prioritization of a German woman. Strikingly, we nd that 57% of the respondents place the priority of the older Indian woman as high or higher than the German woman, and 38% even place it strictly higher."

• We moved this paragraph to the Results section.

* Were participants made aware of the cost of vaccines? The mismatch between money vs. vaccine contributions may be due to participants not knowing the average cost of vaccine doses.

• We did not tell the respondents directly about the average costs of vaccine doses. However, we stated that around 11 billion vaccine doses would be needed globally and that the costs to cover these would be around 70 billion (see Figure 5). So the respondents had an idea about the actual costs of one vaccine dose.

Reviewer #2: (No Response)

Attachment

Submitted filename: Response_to_Reviewers.pdf

Decision Letter 2

Sara Rubinelli

15 Nov 2022

Public support for global vaccine sharing in the COVID-19 pandemic: Evidence from Germany

PONE-D-22-09640R2

Dear Dr. Geissler,

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Sara Rubinelli

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Additional Editor Comments (optional):

Reviewers' comments:

Acceptance letter

Sara Rubinelli

21 Nov 2022

PONE-D-22-09640R2

Public support for global vaccine sharing in the COVID-19 pandemic: Evidence from Germany

Dear Dr. Geissler:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

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on behalf of

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Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

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    S3 File

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    Attachment

    Submitted filename: Response_to_Reviewers.pdf

    Data Availability Statement

    Data and replication material is available at https://wzb-ipi.github.io/vaccine_solidarity/.


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