Willingness to receive a COVID-19 booster vaccine: the role of health literacy and the 7Cs model

Abstract

Vaccination is a modifiable behaviour resulting from a complex decision-making process influenced by a wide range of factors, including the ‘7Cs’ model (confidence, complacency, constraints, calculation, collective responsibility, compliance, and conspiracy) and the ability to find, understand, evaluate and use vaccine information. This work aimed to analyse the intention to receive a booster dose of the COVID-19 vaccine in Spain in the subsequent rollout of the COVID-19 vaccination campaign and how it was influenced by COVID-19 vaccination health literacy and the ‘7Cs’ determinants of vaccine hesitancy. A descriptive cross-sectional study was conducted in February 2022 using an online survey. The sample comprised 1067 participants aged 18 or older, representative of the Spanish general population. Willingness to receive an additional booster dose of the COVID-19 vaccine was assessed using a single yes/no answer question. Determinants of vaccine readiness were evaluated through seven statements aligned with the 7Cs model, adapted to the COVID-19 context. A multivariable logistic regression showed that vaccination intention was influenced by Confidence (OR = 3.79; 95% CI = 2.58–5.58), Calculation (OR = 0.63; 95% CI = 0.45–0.90), Collective Responsibility (OR = 0.52; 95% CI = 0.32–0.86), Compliance (OR = 2.10; 95% CI = 1.42–3.09), Conspiracy (OR = 0.46; 95% CI = 0.29–0.74), and vaccine related HL (OR = 1.03; 95% CI = 1.02–1.06). Fostering vaccination health literacy, strengthening trust in science and health professionals, fighting misinformation and enhancing collective responsibility are relevant aspects for designing effective vaccination campaigns.

Introduction

Vaccination is the main tool for primary prevention of infectious diseases and one of the most cost-effective public health measures available [1]. The COVID-19 vaccination strategy during the pandemic was very successful in Spain, which has been one of the leading countries in COVID-19 vaccination rates [2]. The COSMO-Spain project was monitoring COVID-19 vaccination readiness and reasons for vaccine hesitancy from the early stages of the pandemic [3]. This study showed an increase in the population’s willingness to be vaccinated once the vaccination campaign began, and the highest vaccine acceptance was reached in November 2021 with 96% of the population already vaccinated or willing to get the vaccine [4]. Yet, similarly to other countries and, despite the overall high acceptance of the vaccines, there was an increase of hesitancy regarding upcoming booster dosses [3, 5–8].

Vaccine hesitancy has been defined as a ‘delay in acceptance or refusal of vaccination despite availability of vaccination services’ [9, 10]. Vaccination is a changing behaviour resulting from a complex decision-making process, and there is increasing evidence supporting the need to conduct behavioural studies to identify the drivers of suboptimal vaccine acceptance and uptake within specific populations, thereby ensuring that appropriate and targeted interventions can be implemented in response [11, 12]. Determinants of vaccine readiness have been grouped in the theoretical ‘7Cs’ model as Confidence, Complacency, Constraints, Calculation, Collective responsibility, Compliance, and Conspiracy [9, 13]. Confidence comprises the perception of safety and efficacy of vaccines and the trust in the system in charge of the delivery; Complacency entails not perceiving diseases as high risk and vaccination as necessary; Convenience or constraints include the physical and psychological barriers to vaccination; Calculation is the individual’s engagement in extensive information searching; Collective responsibility, the tendency to consider the protection of others; Compliance as the agreement with health mandates and social norms, and Conspiracy thinking as the belief in fake news related to vaccination. Confidence, collective responsibility, and compliance are positively related to vaccination readiness, while complacency, constraints, calculation, and conspiracy do so negatively. Vaccination health literacy (VHL) is defined as ‘individuals’ knowledge, motivation, and skills to find, understand, and evaluate immunization-related information to make adequate immunization decisions’, has been shown to influence people’s hesitancy regarding vaccination [14].

Although the COVID-19 pandemic is widely considered to be over, booster vaccination remains fundamental to protect people from SARS-CoV-2 infection, hospitalization, and severity [15, 16], and as long as additional doses are recommended, it remains necessary to gain insights into COVID-19 vaccine hesitancy.

This work aimed to analyse the intention to receive a booster dose of the COVID-19 vaccine in Spain in the subsequent rollout of the COVID-19 vaccination campaign and how it was influenced by the 7Cs determinants and COVID-19 vaccination health literacy (CVHL).

Methods

Setting and study population

This observational cross-sectional study analyses data from an online survey conducted in February 2022. The sample, comprised of 1067 participants, was stratified to match the Spanish general population in terms of age, education, gender, and area of residence. Members of a panel were recruited by a consumer research company from among those who fit the inclusion criteria (18 years or older and able to answer an online questionnaire), obtaining a response rate of 82.9%. The sample was weighted with a weighting efficiency of 96.8% and a sampling error of 3.02%.

This study is part of a larger project, the Spanish COVID-19 Snapshot Monitoring (COSMO-Spain), a behavioural insights initiative that conducted population surveys every 2 months between 2020 and 2022. The project was designed to inform the COVID-19 outbreak responses by providing evidence to guide policies, interventions, and communication strategies. The results have been shared with the Spanish health authorities and are publicly available (https://portalcne.isciii.es/cosmo-spain/).

Variables and instruments

The survey collected data on sociodemographic variables (sex, age, education level, rural/urban household, and employment) in addition to the main study variables.

Willingness to get an additional booster dose of the COVID-19 vaccine was assessed using a single yes/no answer question: ‘If health authorities recommended another booster dose of the COVID-19 vaccine, would you get it?’.

The vaccination readiness determinants were assessed by asking participants to agree or disagree with seven statements covering the 7Cs components of vaccination [9, 13]. Original items were translated and back-translated into Spanish and adapted to refer to the COVID-19 vaccine. Responses were graded on a 5-point Likert scale, where 5 indicated ‘strongly agree’ and 1 indicated ‘strongly disagree’ and recoded considering answers from 1 to 3 as ‘disagree’ and 4 and 5 as ‘agree’.

The COVID-19 Vaccine Health Literacy Questionnaire (CVHL-Q) was recently validated in Spain [17] and measures perceived capacity to find, understand, assess, and use COVID-19 vaccine information with a 4-category Likert scale: very difficult (1), difficult (2), easy (3), and very easy (4). The total CVHL score was obtained to indicate the level of COVID-19 Vaccine health literacy, with higher scores indicating better health literacy. CVHL was standardized from 0 to 50; CVHL-index (mean − 1) × (50/3).

Statistical analysis

Descriptive statistics [frequencies, percentages, means, and standard deviation (SD)] were used. Bivariate (chi-square test, Student t-test, Mann–Whitney U test, chi-square test of independence, ANOVA) and multivariable logistic regression analysis (backward stepwise procedure) were performed to analyse how sociodemographic characteristics, 7C determinants of vaccination readiness and CVHL were associated with the willingness to receive a booster dose of the COVID-19 vaccine (Yes/No). We computed the odds ratios (ORs) and 95% confidence intervals (CIs) and considered P values of <.05 to be statistically significant. Analysis was performed using IBM SPSS Statistics version 24 (IBM, Armonk, NY).

Results

Participants’ mean age was 46.52 (SD: 15.222; range: 18–82) years old. Most sample participants had secondary or university studies, and half of the participants were women (Table 1).

Table 1.

Sociodemographic characteristics and willingness to receive a new booster dose

	Total		If health authorities recommended another booster dose, would you get it?
Variables	N	%	Yes, N (%)	No, N (%)	P value
Total	1067	100	776 (72.7)	291 (27.2)
Sociodemographic
Gender					.307
Male	533	50	395 (50.9)	108 (37.1)
Size of urban nucleus	984	92.2
Town/village	202	20.5	149 (19.2)	53 (18.21)	.418
City	222	22.5	168 (21.6)	54 (18.5)
Capital city	179	18.1	139 (17.9)	40 (13.74)
Others	381	38.7	303 (39.0)	78 (26.8)
Employment	992	93
Employed	523	52.7	400 (51.5)	123 (42.2)	.139
Unemployed	187	18.8	147 (18.9)	40 (13.7)
Student	81	8.16	61 (7.86)	20 (6.87)
Retired	159	16.0	131 (16.8)	28 (9.62)
Others	42	4.23	27 (3.47)	15 (5.15)
			Mean (SD)	Mean (SD)	P value
Age	1020	95.59	47.58 (15.02)	43.81 (15.19)	<.001

Most of the participants (n = 776; 72.7%) were willing to receive another booster dose of the vaccines if recommended by health authorities. Significant differences were identified regarding age.

Table 2 shows, for each of the 7Cs, the percentage of subjects who agreed with the statement, along with the proportion of those who would or would not receive a new booster dose and the mean levels of CVHL.

Table 2.

COVID-19 vaccination health literacy, 7Cs, and vaccination readiness

	Total		If health authorities recommended another booster dose, would you get it?
Variables	N Agree	%	Yes, N (%)	No, N (%)	P value
			776	291
7C Agreement
Confidence. I have no doubts about the safety of the COVID-19 vaccines	614	57.5	542 (69.8)	61 (20.96)	<.001a
Complacency. Vaccination against COVID-19 is unnecessary because COVID-19 is not serious anymore	119	11.2	55 (7.08)	37 (12.71)	<.001a
Constraints. Everyday stress prevents me from getting vaccinated against COVID-19	96	9.0	56 (7.21)	26 (8.93)	.046a
Calculation. When I think about getting vaccinated against COVID-19, I weigh benefits and risks to make the best decision possible	523	49.0	365 (47.03)	120 (41.23)	.176
Collective responsibility. When everyone is vaccinated against COVID-19, I don’t have to get vaccinated too	135	12.7	70 (9.02)	44 (15.1)	<.001a
Compliance. It should be possible to sanction people who do not follow the vaccination recommendations by health authorities	506	47.5	444 (57.21)	57 (19.58)	<.001a
Conspiracy. Vaccines cause diseases and allergies that are more serious than the diseases they ought to protect from	162	15.2	68 (8.76)	53 (18.21)	<.001a
COVID-19 Vaccination Health Literacy
CVHL index	Mean (SD)		Mean (SD)	Mean (SD)	P value
	35.29 (11.5)		36.87 (9.6)	28.27 (12.6)	<.001b

^aChi-squared test.

^bMann–Whitney U test.

Regarding the seven determinants of vaccination readiness, high Confidence, Compliance and Collective Responsibility, and low Complacency, Constraints, and Conspiracy thinking showed statistically significant differences in favour of taking the recommended booster dose (Table 2).

In the logistic regression (Table 3), the factors that positively influenced vaccination intention were Confidence—‘I have no doubts about the vaccine’ (OR = 3.79; 95% CI = 2.58–5.58), Compliance—‘It should be possible to sanction people who do not follow the vaccination recommendations’ (OR = 2.10; 95% CI = 1.42–3.09), Collective Responsibility—‘When everyone is vaccinated against COVID19, it will no longer be necessary for me to get vaccinated’ (OR = 0.52; 95% CI = 0.32–0.86), and vaccine-related HL (OR = 1.03; 95% CI = 1.02–1.06). While Calculation—‘When I think about getting vaccinated against COVID-19, I weigh the benefits and risks’ (OR = 0.63; 95% CI = 0.45–0.90) and Conspiracy—Vaccines cause diseases and allergies that are more serious than the diseases they ought to protect from (OR = 0.46; 95% CI = 0.29–0.74), had a negative relationship with the intention of getting a booster dose.

Table 3.

Factors associated with vaccination willingness^a

If health authorities recommended another booster dose of the vaccine, would you get it? Yes/No
	P value	Exp(B)	CI 95% exp(B)
			Lower	Upper
Confidence	<.001	3.79	2.58	5.58
Calculation	.010	0.63	0.45	0.90
Collective responsibility	.011	0.52	0.32	0.86
Compliance	<.001	2.10	1.42	3.09
Conspiracy	.002	0.46	0.28	0.74
CVHL-index	<.001	1.04	1.02	1.06
Constant	.01	0.50

^aLogistic regression adjusted by age.

Discussion

This study was developed in the later rollout of the vaccination campaign in Spain, when, according to health authorities, 90.8% of the Spanish population had received the full dose of the vaccine and 76.5% of people over 40 years of age had already received a booster dose [18]. To the best of our knowledge, this is the first study to examine how HL and the 7C model influence vaccine acceptance in the Spanish population in the context of a pandemic.

Most of the participants (72.7%; n = 776) were ready for a new booster dose if health authorities recommended it. This percentage of readiness is in accordance with the international literature regarding the booster dose [5]. Although several studies have shown during the pandemic that being employed and having a high education level are associated with better vaccine acceptance [7, 19–21], we did not find such relationships. Nevertheless, further analysis of sociodemographic predictors could provide useful insights for more targeted policy recommendations. In recent years, numerous studies have analysed how the 7Cs determinants of vaccination and health literacy (HL) have influenced vaccination behaviour regarding the different COVID-19 vaccine doses among various population groups, with mixed results [9, 13, 19, 22, 23]. Importantly, these studies have highlighted how these determinants—and the associated behaviours—can be improved through culturally appropriate and tailored interventions [11].

According to the logistic regression analysis, the factors that significantly influenced the intention to receive an additional booster dose were Confidence, Calculation, Collective Responsibility, Compliance, Conspiracy Beliefs, and Vaccination Health Literacy.

Similar to other studies [24], Confidence is the strongest predictor of vaccination willingness. The Spanish population has been shown to have a high level of trust in science [25] and in the health system [4], which may have influenced vaccination acceptance. Additionally, confidence in healthcare professionals’ recommendations was stronger in Spain compared to the rest of the European Union [26], making it a key factor and a major driver of vaccine acceptance [4]. This trust, combined with a universal health care system, has played a crucial role in Spain’s high COVID-19 vaccination uptake [4]. Confidence includes high trust in the COVID-19 vaccines and the authorities that recommend vaccination, but also low trust in fake news and conspiracy theories [27, 28]. A previous work in Spain focused on the non-vaccinated population and identified a heterogeneous group of reasons for COVID-19 vaccine reluctance, related to belief in conspiracy theories such as that COVID-19 vaccines modify DNA, and concerns about vaccine safety because of the speed of development [29]. Although weaker, Calculation is another determinant that influences hesitancy in this study, in consonance with the results from other international studies [19, 24, 30]. The Behavioural and Social Drivers (BeSD) of Vaccination framework developed by the WHO [12] closely aligns with the 7C model and highlights the complex role of trust in vaccination behaviour, as well as how confidence, conspiracy and calculation interact to influence hesitancy. The infodemic surrounding COVID-19 [31] has demonstrated society’s vulnerability to health-related misinformation, disinformation and conspiracy theories, and how it has affected the population’s preventive behaviour, including vaccination [28]. With the advancement of artificial intelligence, the proliferation of online media and algorithm-driven content, the landscape of public health communication has been significantly shaped, creating challenges to COVID-19 booster dose uptake. Large-scale randomized control trials showed that exposure to COVID-19 vaccine misinformation depresses vaccination intent, underscoring the susceptibility of undecided audiences to misleading claims [28]. Fake news in general spreads faster and farther than truth, amplifying availability and perceived consensus [32]. Taken together, these mechanisms—algorithmic personalization, homophily-driven reinforcement, and attention-based ranking—can heighten calculation-based hesitancy, erode institutional trust, and bias risk–benefit appraisals against additional doses.

Appealing to Collective Responsibility has been one of the key points of the EU/Spanish vaccination strategy [33, 34], playing an important role in adherence to preventive measures and vaccination acceptance in Spain and other countries. Compliance refers to the willingness to adhere to preventive health behavioural rules and provisions, and in Spain, adherence to health authorities’ recommendations was very high during the pandemic [35]. This is in accordance with the important role of social norms as a primary way to improve compliance with COVID-19 health regulations [12, 36].

Several studies have identified Health Literacy and Vaccination Health Literacy as strong predictors of vaccination intention, including the willingness to receive a COVID-19 booster dose [14]. In this context, bolstering population health literacy—through clear communication, decision-support tools, training in digital and media health literacy—should build trust in vaccines and institutions, counter complacency stemming from risk misperception, reduce the cognitive load associated with calculation, foster collective responsibility, promote compliance with recommendations, and decrease susceptibility to conspiracy narratives [31].

Our study has several limitations. First, the generalizability of our findings is constrained by the fact that online data collection introduces a bias. Secondly, the outcome measure focuses on self-reported intention, not actual behaviour, thus restricting its predictive capability. Likewise, the cross-sectional design of the survey limits our ability to track changes in the 7Cs determinants over time. While this design is less suited for capturing temporal variability, it still allows for the assessment of associations between these antecedents and vaccine-related behaviour. Due to the challenges associated with collecting longitudinal data, our analysis relies on cautious interpretation of the frequency distributions of 7C-related attitudes. Despite the aforementioned limitations, the absence of prior data highlights the value of this study as a foundation for future longitudinal research on vaccine acceptance and promotion in epidemic scenarios.

Conclusions

This is the first study to examine how health literacy and the 7C model relate to vaccine acceptance in the Spanish population in the context of a pandemic. Vaccination has historically maintained high acceptance rates in Spain and a majority of participants expressed their willingness to accept an additional booster if recommended by health authorities. While the relative influence of different factors within the 7C framework may vary depending on time, vaccine type, cultural context, and population, the present findings highlight the potential relevance of vaccination health literacy, confidence in science and health professionals, perceptions of risk, and collective responsibility as dimensions associated with booster vaccination intentions. The evidence of associations between these dimensions and booster vaccination willingness should not be interpreted as causal. The absence of prior data on these associations underscores the value of this study as a foundation for future research on vaccine acceptance in epidemic scenarios.

Author contributions

María Falcón (Conceptualization, Formal analysis, Investigation, Methodology, Writing—original draft, Writing—review & editing), Carmen Rodríguez-Blázquez (Conceptualization, Data curation, Formal analysis, Investigation, Writing—review & editing), Martina Fernández-Gutiérrez (Formal analysis, Writing—original draft, Writing—review & editing), Pilar Bas-Sarmiento (Formal analysis, Writing—original draft, and writing—review & editing), Maria João Forjaz (Conceptualization, Investigation, Writing—review & editing), and María Romay-Barja (Conceptualization, Investigation, Methodology, Writing—review & editing)

Conflict of interest: The authors declare that they have no conflicts of interest.

Funding

This work was supported by the Carlos III Health Institute. The funder had no role in the study design; collection, analysis, and interpretation of data; writing of the paper; and/or decision to submit for publication. Likewise, the publication of this manuscript has been funded by the University of Cadiz.

Data availability

The data underlying this article will be shared on reasonable request to the corresponding author.

Ethical approval statement

The study received ethical approval from the Carlos III Health Institute Ethics Committee (CEI PI 59_2020-v2). Respondents were informed about the aims of the study, and participation consent was given by agreeing to complete the questionnaire.

AI statement

Neither generative AI nor AI-assisted technologies in scientific writing have been used in the writing process of the manuscript.

Key Points.

• Despite the COVID-19 pandemic being under control, vaccination is still underway, and studies indicate that vaccine hesitancy to booster doses is increasing.

• The development and evaluation of interventions to enhance vaccine promotion must be based on a comprehensive model that incorporates, at a minimum, the 7Cs determinants.

• Promoting health literacy about vaccines, strengthening trust in science and health professionals, combating misinformation, and enhancing collective responsibility are relevant aspects that can help design appropriate information and vaccination campaigns for current or future vaccines.