Vaccine hesitancy in the vaccination of children in Brazil

Abstract

Since 2016, there has been a decrease in vaccination coverage for the childhood schedule of the National Immunization Program (PNI) in Brazil. To identify the reasons for vaccine hesitancy, we conducted a household survey of 31,001 live-born children living in the 26 Brazilian state capitals and the Federal District in 2017 and 2018. Census tracts were stratified according to socioeconomic status, we interviewed parents and/or guardians to collect information on the mother, child, reasons for not vaccinating, and other data. To identify the determinants of vaccine hesitancy, were used the “5Cs” (confidence, complacency and convenience, communication and context). Confidence: 94.5 % of parents/guardians of children trust the vaccines; 98.4 % believe it is important to vaccinate their children, and 20,0 % believe that vaccines are associated with serious adverse events. Complacency: 96.7 % decided to vaccinate their children with all the vaccines recommended; 7.2 % experienced difficulties with vaccination (distance and opening hours of the vaccination service, lack of time, problems with the child's health) despite going to the vaccination appointment; 22.9 % did not vaccinate their children (vaccine unavailable, clinic closed, health care provider absent, fear of adverse events). Communication: 24.5 % decided not to take their child for vaccination because of the pandemic; 24.4 % feared a reaction to the vaccine, and 9.2 % did not have the vaccine recommended by their doctor or health care provider. Socioeconomic status: vaccine confidence was lower among mothers with low education levels and lower-income families. Conclusions: Operational difficulties in the health care network were the main reasons for vaccine hesitancy in Brazilian state capitals during the study period. Although the proportion of parents/guardians who do not vaccinate their children voluntarily is low, this is a problem that needs to be consider so that it does not increase over time due to the infodemic.

1. Introduction

Vaccination became a priority in Brazil after the National Program for Immunization (PNI) was launched in 1973. The strengthening of the PNI, especially after the 1990s, when the program was adapted to political, epidemiological and social changes, established vaccination as one of the most important public health interventions and had a positive impact on the morbidity and mortality profile of the Brazilian population [1,2]. In addition, the PNI has helped to reduce regional and social inequalities by providing free vaccination to all Brazilians [1].

Despite the achievements of the PNI, significant challenges have emerged. Many vaccine-preventable diseases have become relatively unknown because they have been controlled or eliminated, leading to a lack of awareness of their seriousness and a belief that vaccines are no longer needed, with the consequent risk of reintroduction or re-emergence of such preventable diseases. Thus, we began to observe a decline in the achievement of recommended vaccination coverage (VC) goals, especially from 2016 onwards, a trend observed not only in Brazil but also in other countries [[3], [4], [5], [6], [7]]. Outbreaks and re-emergence of vaccine-preventable diseases, such as measles, have been reported in subpopulations where VC is below established thresholds due to vaccine hesitancy [8].

Since 2012, the World Health Organization (WHO) has been working to overcome vaccine hesitancy and develop strategies address it. Vaccine hesitancy is a complex issue influenced by cultural, social and economic factors, which vary by time, location and vaccine type provided by different national immunization programs. Due to the complexity of the issue, the WHO established a working group within its Strategic Advisory Group of Experts on Immunization (SAGE). Vaccine hesitancy spans a spectrum from partial acceptance to deliberate delays or outright refusal of vaccines [9]. The Working Group decided to include in its analyses other aspects that reduce VC, such as operational problems and access difficulties. By 2019, the WHO listed vaccine hesitancy as one of the top ten global health threats [10].

To achieve WHO Global Vaccine Action Plan VC targets, countries must address vaccine hesitancy. High hesitancy reduces demand, though low hesitancy does not ensure high demand [11]. Therefore, to achieve high individual and community demand, it is essential to investigate vaccine hesitancy reasons and understand underlying social and cultural contexts. The aim is to develop specific strategies, tailored to the characteristics of each population, to stimulate and strengthen communities' understanding of vaccine importance. Such strategies should explain vaccines benefits and risks of low coverage, helping individuals and communities understand that hesitancy is legitimate but need not be encouraged. With appropriate communication, vaccine uptake can increase, ensuring national immunization targets are met. Additionally, operational barriers contributing to hesitancy must be assessed and addressed to overcome challenges in completing immunization schedules.

Few Brazilian studies have examined the reasons for refusal or delay in the administration of vaccines recommended by the PNI. Therefore, with the encouragement of the PNI, a vaccination coverage survey was carried out to investigate the reasons for non-vaccination and/or incomplete vaccination schedules among Brazilian children. The aim of this publication is to report and discuss the results of the Vaccination Coverage Survey on vaccine hesitancy among children born in 2017 and 2018, living in the 26 state capitals and the Federal District.

2. Material and Methods

The methodology of the vaccination coverage and hesitancy survey was described in Barata et al., 2023 [4]. Briefly, a sample of 32,996 live-born children from the 2017 and 2018 birth cohorts was defined and selected according to socioeconomic strata, including residents of the 26 state capitals and the Federal District (DF). To minimize bias, inverse probability weighting was applied based on demographic data from the census to adjust for non-response.

The study was approved by the Human Research Ethics Committees of the Instituto de Saúde Coletiva da Universidade Federal da Bahia, opinion No. 3,366,818, on June 4, 2019, with Certificate of Submission for Ethical Appraisal (CAAE) 4,306,919.5. 0000.5030, and the Irmandade da Santa Casa de São Paulo, opinion No. 4.380.019, issued on November 4, 2020, with CAAE 39412020.0.0000.5479.

Through home interviews, we collected socio-demographic data of the child and mother, data on household and family consumption, reasons why parents did not vaccinate, barriers to vaccination, reasons for not being vaccinated despite seeking services, and parents' views on vaccines. Following the interview, we collected data on vaccines administered and dates of administration during the first 24 months of the child's life from Vaccine Registration Cards.

To understand vaccine hesitancy, defined as delaying or refusing vaccination even when the vaccine is available, we used the WHO SAGE Committee classification, which provides a conceptual model of the determinants of vaccine hesitancy. The classification model is based on the “3Cs”: Confidence, Complacency and Convenience” [11]. Confidence is defined by: (i) the efficacy and safety of vaccines; (ii) the system that delivers them, including the reliability and competence of health services and professionals; and (iii) the motivations of policy-makers who decide which vaccines to use in national immunization programs [11]. Complacency occurs when the risks of vaccine-preventable diseases are perceived to be low and vaccination is seen as an unnecessary preventive measure. Convenience includes factors such as: distribution of vaccines; availability of vaccines in health services and/or willingness to pay for them; geographical accessibility; ability of the population to understand the importance of vaccination; commitment of services to ensure population adherence; quality of services (real and/or perceived) and the extent to which vaccination services are provided at a given time and place; and the cultural context of a population, which may also influence the decision and lead to vaccine hesitancy [11]. The WHO's 5C model for characterizing vaccine hesitancy includes issues such as difficulty accessing health services or personal barriers to vaccination, categorized as convenience. Although these aspects are not always viewed as hesitancy, which is defined by uncertainty or reluctance to vaccinate, they were considered as hesitancy in this study to enable the comparison of this survey with data from studies conducted in other countries.

Razai et al., 2021, proposed the inclusion of another “2Cs” in this conceptual model, one of them being Communication, as the authors considered that the world is experiencing an epidemic of not always reliable information (“infodemic”), generating mistrust, uncertainties, speculation and fears, which promote vaccine hesitancy. This scenario, which became more apparent during the Covid-19 pandemic, must be overcome through a real and transparent dialogue, supported by society, aimed at deconstructing this unfavorable consequence. The authors highlighted the fact that socio-economic, demographic and ethnic variables are also determinants of vaccine uptake, so they included Context as another component of the conceptual model of vaccine hesitancy. Thus, the present study incorporated the “5Cs” [12].

3. Data analysis

All point estimates and their respective confidence intervals were calculated using STATA, version 16, Survey Data Analysis module, taking into account the sample weights and the study design. Details of the statistical analysis are described in Barata et al. (2023) [4].

4. Results

Of the 32,996 live-born children selected, interviews were conducted with 31,001 parents and/or guardians, representing 94.0 % of the originally planned sample. Losses accounted for 6.0 % of the sample, primarily due to the inability to locate children within the same cluster, refusals, and duplicate records. The highest losses occurred in stratum A (18.8 %), followed by stratum B (6.4 %), while no losses were observed in strata C and D. The distribution of responses by Brazilian regions was 97 % for the Central West region and North region, 96 % for the Northeast and Southwest regions, and 86 % for the South region. The reasons for non-vaccination were analyzed according to the “5Cs” determinants of vaccine hesitancy, as described in methods [4,11].

4.1. Confidence

Across state capitals, 94.5 % of parents/guardians trusted government-provided vaccines, and over 98 % agreed vaccines were important for their children's health, with no significant differences among social strata. However, 20 % associated vaccines with serious adverse reactions, ranging from 12 % in stratum A to 24.5 % in stratum D (Table 1).

Table 1.

Assessment of Confidence in the PNI (%), according to socioeconomic strata, Brazilian capitals and DF^⁎

Socioeconomic Strata⁎⁎	Confidence in vaccines provided by the government %(CI95%)	Importance of vaccines for children's health %(CI95%)	Vaccines produce severe adverse reactions %(CI95%)
A	95.6 (92.9;97.4)	98.4 (96.8;99.2)	12.0 (9.2;15.7)
B	94.9 (93.0;96.3)	97.7 (94.4;99.1)	13.5 (10.5;17.1)
C	95.3 (93.6;96.6)	99.0 (98.3;99.5)	15.8 (13.5;18.3)
D	94.0 (92.4;95.3)	98.2 (97.1;98.9)	24.5 (21.2;28.2)
Total	94.5 (93.5;95.4)	98.4  (97.7;98.8)	20.0 (17.9;22.2)

^⁎2020 vaccination coverage survey performed with children born in 2017 and 2018.

^⁎⁎Strata: A, B, C, D.

4.2. Complacency

Vaccination of their children at least once was reported by 96.6 % of parents or guardians, with differences among socioeconomic strata. Families in stratum D had the highest intention to vaccinate their children (95.8 %), followed by those in stratum B (96.5 %). Thus, most parents or guardians reported that they had decided to give their children all the vaccines recommended by the PNI, although about 3.5 % of the population surveyed had deliberately chosen not to vaccinate their children. Regarding the perceptions of the parents/guardians of the children, when asked about the “need for vaccination against diseases that no longer exist”, 80.2 % of the parents/guardians responded that it was necessary to continue vaccination against these diseases. We found that the proportions of responses differed when the four strata were compared: only 75.1 % in stratum D agreed and stated that vaccination against diseases that no longer exist is necessary. The proportion was 84.9 % in stratum B, 86.6 % in stratum C and 89.0 % in stratum A. Regarding the importance of vaccination for collective protection, 97.1 % of the guardians agreed with the statement that “vaccinating children is important for the health of the children in the neighborhood”, with the lower proportion of agreement registered in stratum B (95.6 %) (Table 2).

Table 2.

Assessment of Complacency towards PNI actions, according to socioeconomic strata. Brazilian capitals and DF^⁎

Socioeconomic Strata⁎⁎	Decision to vaccinate child %(CI95%)	Need of vaccines for no longer existing diseases %(CI95%)	Importance of vaccines for the collective health of the neighborhood %(CI95%)
A	97.3 (95.9;98.2)	89.0 (86.3;91.2)	97.3 (95.5;98.4)
B	95.8 (93.1;97.5)	84.9 (81.4;87.8)	95.6 (92.7;97.4)
C	97.2 (96.0;98.0)	86.6 (83.9;87.8)	97.7 (96.2;98.6)
D	96.5 (95.4;97.4)	75,1 (70.1;79.6)	97.2 (96.1;98.0)
Total	96.6 (95.9;97.2)	80.2 (77.2;82.9)	97.1 (96.4;97.7)

^⁎2020 vaccination coverage survey performed with children born in 2017 and 2018.

^⁎⁎Strata: A, B, C, D.

4.3. Convenience

We found that, on average, 7.2 % of parents or guardians reported difficulties for taking their children for vaccination. For participants in stratum D, the proportion reported was 8.2 %, although the difference between participants in stratum D and the other strata was not significant. The inability to vaccinate, even if the child had been taken to the vaccination service on the correct date, was reported on average by about 23 % of respondents, ranging from 20.8 % in stratum A to 23.9 % in stratum C, with no statistically significant difference among strata (Table 3).

Table 3.

Assessment of Convenience of PNI actions, according to socioeconomic strata. Brazilian capitals, and DF^⁎

Socioeconomic Strata⁎⁎	Had difficulties taking the child to be vaccinated %(CI95%)	Failed to vaccinate child despite going to the vaccination center %(CI95%)
A	5.5 (4.1;7.4)	20.8 (17.2;24.9)
B	7.2 (5.1;10.1)	22.4 (19.2;26.0)
C	5.2 (4.2;6.4)	23.9 (21.3;26.8)
D	8.2 (6,8;10.0)	23.1 (20.4;26.1)
Total	7.2 (6.3;8.2)	22.9 (21.2;24.8)

^⁎2020 vaccination coverage survey performed with children born in 2017 and 2018.

^⁎⁎Strata: A, B, C, D.

Table 4 outlines the main obstacles reported by parents and/or guardians for taking their children for vaccination. Among 7.2 % who reported difficulties in getting their children vaccinated, 93.8 % cited operational issues like distance and inconvenient opening hours. Personal obstacles, such as lack of time, or a child's health problem were mentioned by 84.8 %. Respondents could select multiple reasons, so the totals in Table 4 refer to the number of responses received and not to the number of individuals interviewed.

Table 4.

Operational and personal problems related to difficulties in taking children to the vaccination service, Brazilian capitals and DF^⁎

Problems	n	%
Operational Problems
Vaccination clinic far from home or work	1,047	56.2
Opening hours of the vaccination clinic are inadequate	700	37.6
Lost or does not have a vaccination card	98	5.3
Other reasons	17	0.9
Total	1,862	100.0
Personal Problems
Lack of time to take the child to the vaccination clinic	1,047	47.3
Child with a health problem (acute or chronic illness)	830	37.5
My boss does not allow me to leave work	167	7.5
Transportation issue (lack of money or transport)	110	5.0
Other reasons	60	2.7
Total	2,214	100.0

^⁎2020 vaccination coverage survey performed with children born in 2017 and 2018.

The main reasons for not being vaccinated despite attending the vaccination service were unavailability of vaccine (44.1 %); closed vaccination service (10.8 %); health professional did not recommend or missed vaccination (7.9 % and 7.6 %, respectively); and it was not the scheduled date (7.1 %) for a particular vaccination (Table 5).

Table 5.

Reason for not vaccinating, Brazilian capitals and DF^⁎

Reason for not vaccinating	N	%
Reason for not vaccinating, although the child was taken to the vaccination service
Vaccine unavailable	7,569	44.1
Vaccination service was closed	1,857	10.8
Professional did not recommend	1,354	7.9
Lack of healthcare professionals	1,299	7.6
It was not the scheduled date for a particular vaccine	1,217	7.1
There were a lot of people in line, and parent could not wait	1,165	6.8
Lack of vaccination material	1,063	6.2
Vaccination service already overbooked	962	5.6
Parent came for the vaccination appointment, but child was not vaccinated because a document was missing	578	3.4
Other reasons	82	0.5
Total	17,146	100.0
Reasons that contributed for parent deciding not to vaccinate child
COVID-19 pandemic	365	24.5
Fear of vaccine reactions or history of vaccine reactions	364	24.4
Physician or healthcare professional advised not to vaccinate child	137	9.2
I fear giving my child an injection	133	8.9
I do not believe in vaccines	126	8.4
I believe vaccines are bad for health	88	5.9
News spread on social media made me stop vaccinating	73	4.9
The disease no longer exists	66	4.4
Friend or relative advised me not to vaccinate	54	3.6
Forgot to show up to the vaccination appointment	34	2.3
Other reasons	52	3.5
Total	1,492	100.0

^⁎2020 vaccination coverage survey performed with children born in 2017 and 2018.

4.4. Communication

The most common reasons given by respondents for not vaccinating their children were restrictions imposed by the COVID-19 pandemic (24.5 %), fear of vaccine reactions (24.4 %) and physician or health professional not recommending the vaccine (9.2 %). Excluding the COVID-19 pandemic as a reason for not vaccinating, “I do not believe in vaccines”, “I believe vaccines are bad for health”, “I stopped vaccinating because of news on social media”, “the disease no longer exists” together accounted for 23.6 % of responses and were the second reason for not vaccinating (Table 5).

4.5. Socio-economic scenario

Table 6 shows data on socio-economic background, and we found that parents or guardians with incomplete elementary level education, lower income and under 20 years of age were the groups who had less confidence in the vaccines offered by the PNI (90 %, 93 % and 95 % respectively). These groups were also less likely to feel the need to vaccinate their children against diseases that are under control (67 %, 72 % and 74 % respectively). They also reported greater fear of vaccine-related adverse events (29 %, 27 % and 22 % respectively) and lower vaccination rates for their children. Race and gender had no effect on children's vaccination uptake, with only small differences among answers.

Table 6.

Socio-economic setting and factors that contributed to children not being vaccinated^⁎

Socio-economic characteristics	Decision to Vaccinate % (CI95%)	Trust in vaccines provided by Government % (CI95%)	Need to Vaccinate % (CI95%)	Fear of vaccine adverse effects % (CI95%)	Access difficulties % (CI95%)	Took child to Vaccination Service but was not vaccinated % (CI95%)	Vaccine Delay % (CI95%)
Mother's schooling
Incomplete elementary school	96.7 (95.0–97.8)	91.1 (88.0–93.4)	68.5 (62.6–73.8)	28.1 (23.6–33.0)	11.1 (8.7–14.3)	23.2 (19.5–27.4)	67.3 (61.8–72.4)
College	96.9 (95.7–97.7)	96.8 (95.6–97.7)	88.6 (86.1–90.6)	13.2 (11.3–15.3)	5.0 (4.0–6.3)	21.1 (18.7–23.6)	42.4 (39.2–45.6)
Familiar income (US$)⁎⁎
< 200.00	96.3 (95.0–97.2)	93.3 (91.7–94.6)	72.3 (67.8–76.4)	26.6 (23.2–30.3)	9.9 (8.4–11.7)	24.4 (21.8–27.1)	59.1 (56.2–62.0)
> 1600.00	97.6 (96.6–98.3)	96.7 (94.4–98.1)	92.2 (89.2–94.4)	11.7 (8.7–15.6)	7.0 (5.0–9.6)	20.0 (16.5–23.9)	43.6 (38.1–49.3)
Mother's age (years)
<20	96.7 (92.7–98.5)	95.0 (91.7–97.1)	75.8 (67.4–82.7)	20.9 (14.4–29.4)	8.0 (5.0–12.6)	24.7 (17.9–33.1)	64.9 (56.6–72.4)
20–34	96.2 (95.1–97.0)	93.5 (92.2–94.6)	79.4 (76.9–81.8)	20.6 (18.5–23.0)	8.4 (7.1–10.0)	25.8 (23.8–27.9)	54.8 (52.6–56.9)
>35	97.6 (96.9–98.2)	96.2 (95.1–97.0)	82.5 (78.9–85.5)	18.2 (16.0–20.8)	5.4(4.5–6.5)	20.2 (18.2–22.3)	49.7 (28.0–71.4)
Mother's race
White	96.8 (95.7–98.5)	95.5 (94.3–96.5)	81.6 (70.1–84.7)	18.0 (15.4–21.0)	5.0 (4.0–6.4)	17.2 (15.5–19.2)	44.4 (41.7–47.0)
Black	95.6 (92.5–97.4)	93.1 (90.4–95.0)	78.9 (73.7–83.1)	22.6 (18.6–27.2)	8.6 (6.8–100.8)	28.9 (25.0–33.3)	56.2 (51.5–60.9)
Brown	97.1 (96.4–97.6)	94.3 (93.1–95.4)	79.7 (76.6–82.4)	20.8 (18.7–23.1)	8.5 (7.4–9.7)	28.9 (26.7–31.1)	57.8 (55.6–60.0)
Yellow	98.5 (96.3–99.4)	92.4 (82.9–96.9)	87.4 (74.6–94.2)	14.4 (6.6–28.7)	22.5 (9.4–44.8)	24.7 (12.1–43.9)	53.4 (37.6–69.2
First nations	96.8 (91.1–98.9)	98.5 (95.2–99.36)	92.6 (83.5–96.9)	16.5 (7.3–33.1)	5.2 (2.3–11.5)	10.7 (5.6–19.2)	75.7 (64.7–84.1)
Child's sex
Male	96.9 (96.1–97.6)	95.3 (94.4–96.1)	81.5 (78.9–83.8)	19.1 (16.8–21.6)	7.5 (6.4–8.7)	23.3 (21.3–25.3)	52.4 (49.9 (54.8)
Female	96.6 (95.6–97.4)	94.0 (92.7–95.1)	79.5 (75.8–82.7)	20.4 (18.2–22.7)	6.7 (5.6–8.0)	23.4 (21.3–25.6)	50.4 (47.9–52.9)

^⁎2020 vaccination coverage survey performed with children born in 2017 and 2018.

^⁎⁎mean value of US dollar compared to the Brazilian Real in 2022.

5. Discussion

This is one of the most comprehensive studies on vaccine hesitancy in the world, based on data from children's parents and guardians, who play a key role in ensuring childhood vaccination. Despite high support for Brasil's vaccination policy and the credibility of the PNI, vaccine coverage rates in Brazil have been declining in recent years [5], which calls for caution in the analysis of our results, given the complexity of vaccine hesitancy.

In this study, complete vaccination coverage across Brazilian capitals was 59.9 % (95 % CI 58.3; 61.5), while 6.1 % (95 % CI 5.3, 6.9) received no vaccines. By socioeconomic strata, coverage was 53.0 % (95 % CI 47.3, 58.6) in stratum A, 59.0 % (95 % CI 54.0, 63.8) in stratum B, 62.4 % (95 % CI 59.8, 65.0) in stratum C, and 60.6 % (95 % CI 58.3, 62.7) in stratum D. Adjusted analysis showed lower coverage among children in stratum A (OR = 0.68; 95 % CI 0.53–0.87), those with less-educated mothers (OR = 0.70; 95 % CI 0.54–0.90), and those with delayed vaccination by six months (OR = 0.28; 95 % CI 0.24–0.32) [13].

It is important to highlight that the childhood immunization schedule expanded from 7 to 12 vaccines between 2000 and 2015, increasing the required visits to complete the schedule. The average number of visits was 10.8, three more than the PNI recommendation, with 95 % of children needing up to 14 visits to complete [13].

We will first discuss the main findings for each of the “5Cs”. We will then suggest strategies for overcoming the main problems identified.

5.1. Confidence

Most respondents (94.5 %) indicated that they trust PNI vaccines and are aware that they protect the health of their children and the community against certain diseases, suggesting that lack of trust may not be the main reason for the decline in VC in Brazil yet. However, despite the adequate safety profile of the vaccines provided by the PNI and compliance with existing Brazilian legislation, nearly 20 % of parents and guardians believe that vaccines can cause serious side effects. Over time, this perception has the potential to undermine confidence in vaccines, as has been shown in studies conducted in Brazil and abroad [[14], [15], [16], [17]]. Although the perception of side effects may be associated only with certain vaccines, the finding that a high proportion of respondents mentioned it suggests that health managers at the three levels of government urgently need to convey the message that vaccines are very valuable, particularly in reducing morbidity and mortality, without ignoring side effects. The message should aim to increase everyone's commitment to defending vaccination and fighting fake news.

5.2. Complacency

Almost 97 % of parents or guardians had vaccinated their children at least once, and most of them (96.5 %) said they had decided to give their children all the vaccines recommended by the PNI, i.e. only 3.5 % decided not to give one or more vaccines. Although the proportion is low, this type of complacency reveals the attitude of individuals who are not concerned about the risks of not vaccinating, or the lack of urgency to protect their children, which increases the spread of preventable diseases. It also contributes to the incompleteness of the vaccination schedule, as shown by the VC survey conducted at the same time as this study [2] and must be considered when developing strategies to overcome vaccine hesitancy.

It is important to emphasize that complacency assesses the intention to vaccinate, which can be influenced by factors beyond individual will, such as lack of time, difficulty accessing services, among others. We acknowledge that the discrepancy between the high declared intention to vaccinate (96.5 % of parents or guardians reported having decided to administer all vaccines recommended by the PNI) and the lower vaccination coverage rates observed in higher socioeconomic strata is a point that warrants further investigation. It was not within the scope of this study to assess the reliability or honesty of the respondents' answers.

In addition, almost 20 % of respondents believed that there was no need to continue vaccination against eliminated and/or controlled diseases, indicating a high level of complacency in society, which is a major public health concern, as reduced risk perception may reduce collective immunity and facilitate the reintroduction and recirculation of infectious agents.

As other authors and the WHO working group have pointed out [11,18], this is a paradox. When national vaccination programs achieve their goals and have a major epidemiological impact by significantly reducing the incidence of the target diseases [19], vaccination compliance of the population decreases, jeopardizing the gains made after decades of governmental efforts and public support, and creating a more favorable social environment for fake news (anti-science) against vaccines.

A European survey reported that between 12 % and 28 % of parents surveyed were uncertain about vaccinating their children, showing that vaccine hesitancy is a more worrying problem in developed countries [20]. Although only 3.5 % of the population surveyed in the present study reported deliberately not vaccinating their children, it should not be overlooked that the factors discussed above may increase and thus contribute significantly to not achieving the recommended VC.

In Brazil, the progress made between 2000 and 2016 became a benchmark for other countries, as the VC for all vaccines in the childhood immunization schedule reached its targets year after year, allowing the elimination of measles and neonatal tetanus, as well as the control of other vaccine-preventable diseases [5].

These successes stem from continuous, targeted vaccination strategies; the PNI's ability to mobilize populations for routine and campaign vaccinations; expanding vaccination services nationwide; and targeted interventions for isolated groups like riverine communities (populations living along rivers and relying on aquatic ecosystems for their livelihoods), quilombola communities (Afro-Brazilian settlements founded by descendants of escaped enslaved Africans), and indigenous groups.

The inclusion and the introduction of new vaccines after rigorous safety and efficacy assessments, among other initiatives, further strengthened the PNI, making it a model of public policy [1,2,21]. Paradoxically, the success achieved in controlling the incidence of vaccine-preventable diseases has been one of the causes of vaccine hesitancy.

5.3. Convenience

More than 7 % of respondents in our survey also missed at least one vaccination appointment because they did not attend, mainly because of the distance to the service and the service's opening hours. Public vaccination services are only open Monday to Friday, except during campaigns, when the entire vaccination structure of the health services remains open on Saturdays and Sundays and an additional number of vaccination sites are offered. Other studies conducted in Brazil [22,23] have also identified lack of time, forgetfulness and unavailability of vaccines at the health service as reasons for delays in vaccine administration. These logistical problems represent a major failure in the national management of the PNI, which may be due to difficulties in other areas of the health system or to supply shortages on the national and/or international market. At the local level, this may result either from the absence or shortage of vaccinators, or from failure to follow the recommended interval between doses due to limited stocks of some injectable vaccines, such as BCG, thus compromising the completeness of VCs [21].

These operational failures must be urgently addressed, especially for routine immunization services, which require human resources throughout the Brazil's Unified Health System (SUS) primary care network. SUS provides universal, free healthcare, including consultations, exams, hospitalizations, vaccinations, surveillance, and transplants. Its integrated network comprises Primary Health Units (UBS), Emergency Care Units (UPA), hospitals, labs, research centers, and the Mobile Emergency Care Service (SAMU) for emergencies and transport.

In addition, the municipal health services must increase the number of services and/or vaccination points, considering locations that are further away from the health services, to allow access for parents and/or guardians who cannot afford to miss work and/or pay for transportation. The central management of the PNI has the task of ensuring the continuous supply of an adequate quantity of all the necessary inputs, regularly delivered to the health units that administer vaccines. This is not always achieved, and we have reported this serious operational failure at least once for 20 % of children. These children attended the service but were not vaccinated, either because the vaccine was unavailable or because the specific vaccine required was not administered on the scheduled day of the week (e.g. multi-dose BCG vials), resulting in missed vaccination opportunities that could have been avoided. Unfortunately, since 2017, Brazil has experienced continuous vaccine shortages due to supply constraints in the national and international markets [5].

5.4. Communication

The fact that our study was conducted during the Covid 19 pandemic (2020/2021), when the necessary social distancing led to reduced access to several health services, together with the infodemic of misinformation about the Covid 19 vaccine [21], led to a negative impact on all immunization activities.

Millions of children and adolescents suffer from vaccine-preventable diseases annually due to low vaccine acceptance by caregivers. Vaccine hesitancy stems from social and structural barriers, as well as misinformation or deliberate disinformation about vaccines [24].

Misinformation is false information shared without intent to deceive, while disinformation is deliberately created or manipulated to mislead, often to promote a specific narrative or agenda. (National Library in Australia). It significantly shapes attitudes and behaviors, particularly regarding vaccine willingness. Those refusing vaccination often cite misconceptions, mistrust, and perceived lack of necessity as key reasons. The widespread online spread of such false information has been termed a ‘second pandemic,’ fueling crisis mistrust and undermining vaccination efforts [25].

Social media has become a key channel for spreading vaccine misinformation, blurring the line between credible and unreliable sources. A Centre for Countering Digital Hate (CCDH) report criticized platforms for enabling the anti-vaccine movement, noting that anti-vax accounts gained 7.8 million new followers since 2019, with 31 million followers on Facebook and 17 million on YouTube. The movement reportedly generates up to $1 billion annually for social media companies. Online misinformation further impacts vaccine willingness, as individuals exposed to such content face scientific skepticism, emotional appeals to civil liberties, and concerns about children's health. Anti-vaccine messaging fosters community among skeptics, emphasizing themes like safety, alternative medicine, freedom, conspiracy theories, and moral arguments [25,26].

Furthermore, being misinformed differs from being uninformed, as it involves distinct cognitive processes. Given widespread misunderstanding of the scientific method, many surveyed were misinformed about vaccines [27]. Another key point is that widespread misinformation erodes trust in public health authorities, hindering effective communication of vaccine benefits. This leads to declining vaccination rates, outbreaks of preventable diseases, weakened herd immunity, and increased public distrust [28].

Effective community engagement and communication strategies are essential to counter misinformation. Coercive measures, such as vaccine incentives, should only be considered as a last resort after trust-building approaches. Addressing under-vaccination requires a multifaceted, evidence-based strategy that identifies barriers and develops tailored solutions for both inadvertent under-vaccination and vaccine hesitancy [29]. Thereby, to improve vaccine acceptance, it is crucial to provide clear, accessible information about the risks and safety of vaccines, as well as strong evidence of their efficacy [28].

A somewhat disturbing finding was that 9.2 % of children born in 2017 and 2018, with an incomplete immunization schedule, received a contraindication from the health provider for one or more vaccines included in the National Childhood Immunization Schedule. Studies show that parental vaccine hesitancy decreases significantly when providers recommend vaccination [8,16,22].

A study in the state of São Paulo found that half of the missed opportunities to vaccinate (MOV) were due to incorrect contraindications, the most common reason for MOVs. These included common illnesses, history of vaccine-preventable diseases, malnutrition, antibiotic use, stable neurological conditions, family seizure history, low-dose corticosteroids, allergies, prematurity, low birth weight, and hospital admission [30]. This communication gap requires urgent attention with studies focusing on healthcare providers to understand the extent and reasons behing incorrect contraindications. Training should reinforce scientific evidence, regulatory competence, and the critical role of health professionals in protecting children's health, improving communication with parents/guardians to avoid incorrect contraindications.

5.5. Socio-economic scenario

Regarding the socio-economic scenario, the results of the survey are contradictory when the two main subjects of analysis, vaccine hesitancy and vaccination coverage, are examined. The preponderance of more hesitant parents and/or guardians among those with lower income, incomplete elementary level education and under 20 years of age - given that they express less confidence in vaccines, feel less need to vaccinate and are more fearful of vaccine-related adverse events - contrasts with the VC findings, where the lowest rates were always associated with the stratum with the highest socioeconomic level (stratum A).

This scenario highlights the need to better understand how different factors affect different social groups. This understanding is essential for designing aggressive strategies to communicate effectively with specific target groups, as they are not always influenced in the same way. This is undoubtedly one of the major challenges to be met, and one that necessarily involves communication to reach society as a whole and overcome any information barriers.

5.6. Strengths and limitations

Surveys are an excellent tool for assessing coverage, trends and equity in access to health services. They are essential for setting priorities and evaluating the impact of public health interventions.

This population-based study, encompassing diverse socioeconomic strata, was timely, as few Brazilian studies have examined voluntary vaccine refusal or delay under SUS. It compared vaccination coverage (VC) data from parents/guardians with PNI records, identifying barriers to achieving VC targets. Conducted during a pandemic and infodemic marked by widespread anti-vaccine misinformation, the study included vaccine hesitancy questions, revealing key barriers: health service issues, missed vaccination opportunities, perceived risks of adverse events, and lack of perceived need for vaccines against supposedly eliminated diseases.

Conversely, one of the limitations of large surveys is the difficulty in obtaining information from minorities, including indigenous populations, families with no fixed residence, and religious groups that do not adhere to medical technologies [18]. The study had such limitations because the participants were not representative of the general population, which may lead to a lack of generalizability of the results, as it only included urban areas of the state capitals and the Federal District, which cover about 25 % of the children living in the country. Although it is not possible to generalize the data for the country, especially for rural populations, small communities and minority groups, the sample studied describes an important part of the Brazilian population.

In addition to quantitative data on VC using the “5Cs” model, we also sought to understand the extent and reasons for vaccine hesitancy that prevent the achievement of VC levels and completeness. Data were collected based on information obtained directly from the children's caregivers, so the reasons for refusal and/or difficulties in vaccinating children were more reliable. To overcome problems related to the limited time available to answer all questions, interviewers attempted to complete the data collection by telephone after authorization.

6. Conclusions

Operational problems were the main reasons for vaccine hesitancy in Brazilian capitals during the study period. These problems existed even before the restrictions imposed by the Covid-19 pandemic. Although our results showed a very small proportion (3.5 %) of parents and/or guardians who deliberately chose not to vaccinate their children, the main reason for non-vaccination was clearly operational, as about 23 % of respondents reported that they were unable to vaccinate their children with one or more vaccines in the childhood schedule, despite having taken the child to the vaccination service on the scheduled date. This finding highlights recurrent missed opportunities for vaccination, suggesting that the decline in VC observed since 2016 was already somehow related to structural problems in the SUS, which unfortunately began to affect the effectiveness of the PNI, Brazil's best disease control program, internationally recognized as one of the most comprehensive and universal in the world.

This finding calls for a comprehensive debate on the way vaccines are delivered by immunization services in Brazil. Such a debate must take place at the three levels of government, including the participation of non-health sectors, acting synergistically to propose effective guidelines to ensure an adequate structure for the services, while respecting the specific responsibilities of the agency in each state.

It is the task of SUS managers to put forward proposals to minimize, or even eliminate, the operational obstacles inherent in some way to the specificities of this complex immunization program. The lack of human and/or material resources, the shortage of vaccines, the limited number of days and hours that vaccination services are open, and the difficulty of access to the vaccination service are some examples of problems reported in this study that require careful consideration by managers and technicians to avoid unnecessary missed opportunities for vaccination.

Lack of time for parents and/or guardians to take children to vaccination services was a common problem reported by respondents, which is heightened by the millions of informal workers in Brazil and the fact that most households in Brazil are headed by women. Of the 75 million households, 50.8 % have a female head of household, who may not be fully available to go to a health facility on any day or at any time [31]. It is therefore essential to review the adequacy of immunization services, with a view to making them compatible with the daily routines of the majority of the population. Extending the opening hours of primary health services to a third shift, or even opening on weekends and holidays, is a strategy that is already having an impact in some Brazilian cities.

The effective involvement of health care providers is important, especially vaccinators, who deliver vaccines to the entire Brazilian population in every corner of this continental country with such a diverse population. On the other hand, constant communication with society, through all communication media, the implementation of awareness campaigns to prevent or even reverse fake news, the promotion of support and participation in civil society organizations, are initiatives that can lead all Brazilians to be unconditional supporters of the vaccines recommended by the PNI.

Certainly, we have faced several challenges in this study. Only a truly integrated, intra- and intersectoral action, involving the social and educational sectors, will be able to contribute to the restructuring of vaccination services and the recovery of a full vaccination culture in Brazil.

CRediT authorship contribution statement

Ana Paula França: Writing – review & editing, Project administration, Methodology, Data curation, Conceptualization. Carla Magda Allan Santos Domingues: Writing – review & editing, Writing – original draft, Supervision, Methodology, Formal analysis, Conceptualization. Raissa Allan Santos Domingues: Writing – review & editing, Project administration, Methodology, Data curation, Conceptualization. Rita Barradas Barata: Writing – review & editing, Supervision, Methodology, Formal analysis, Conceptualization. Maria da Glória Teixeira: Writing – review & editing, Methodology, Investigation, Funding acquisition, Conceptualization. Ione Aquemi Guibu: Writing – review & editing, Project administration, Conceptualization. José Cássio de Moraes: Writing – review & editing, Writing – original draft, Project administration, Methodology, Funding acquisition, Formal analysis, Data curation, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

Data will be made available on request.