Spatial clustering of low rates of COVID-19 vaccination among children and adolescents and their relationship with social determinants of health in Brazil: a nationwide population-based ecological study

Abstract

Objective

This study aimed to investigate the spatial clusters of high and low COVID-19 vaccination rates among children and adolescents across Brazilian municipalities and their relationship to social determinants of health.

Study design

This is a nationwide population-based ecological study.

Methods

We have obtained for each of the 5570 Brazilian municipalities data on the COVID-19 vaccination rate of children and adolescents by August 16, 2022, the Gini index, the social vulnerability index and the municipal human development index. A Bayesian empirical local model was used to identify fluctuations in the COVID-19 vaccination rates. Spatial clusters were identified using scan spatial statistic tests. The relationship among COVID-19 vaccination rates and social determinants of health was explored by using multiple linear regression models.

Results

Overall, 52.1% of children aged 5–11 years and 72.8% of adolescents aged 12–17 years have been fully vaccinated against COVID-19 in Brazil by mid-August 2022. There was spatial dependence on the smoothed rates for both children (I Moran 0.66; P < 0.001) and adolescent (I Moran 0.65; P < 0.001) groups. The lowest rates occurred in municipalities in the North and Northeast regions. Municipalities with a higher Gini Index, higher social vulnerability index and lower municipal human development index were more likely to have a lower COVID-19 vaccination rate for both children and adolescent groups.

Conclusion

COVID-19 vaccination of children and adolescents was heterogeneously distributed, with spatial clusters of the lowest vaccination rates occurring mainly in municipalities with marked socio-economic disparities and social vulnerability, especially in the North and Northeast regions.

Introduction

COVID-19 vaccines are recommended in Brazil since January 2022 for individuals over 5 years of age. As of August 16, 2022, 61.8% of children and adolescents aged 5–17 years have been fully vaccinated against COVID-19 in Brazil.¹ Since the country has marked social and health inequities, vaccination rates are expected to vary geographically. Furthermore, there is currently limited information on the vaccination distribution and on the existence of spatial clusters of low COVID-19 vaccine coverage among children and adolescents and their relationship to sociodemographic characteristics. Thus, we examined spatial clusters of high and low COVID-19 vaccination rates among children and adolescents across Brazilian municipalities and their relationship to social determinants of health.

Methods

Study design

We conducted a population-based ecological analysis of the spatial distribution of all children and adolescents fully vaccinated against COVID-19 until August 16, 2022. The geographic units of analysis were the municipalities, and we included all the municipalities of the country. We examined the relationship between the municipalities' COVID-19 vaccination rate and social determinants of health. All analyses were performed considering the children and adolescents’ residence data.

Data sources and measures

Data were obtained from a variety of publicly available databases. Data on COVID-19 vaccination were obtained from OpenDataSUS.¹ This database has the vaccination records per municipality for all children (aged 5–11 years) and adolescents (aged 12–17 years). The number of children and adolescents for 2021 by age and municipalities was obtained from the Brazilian Ministry of Health's estimate. This population estimate is the same one used by municipal health departments to plan vaccine doses for the target population. Gini Index and Municipal Human Development Index (MHDI) by municipality were obtained from the 2010 Brazilian Census. The Gini index measures the degree of income concentration in a population group and ranges from 0 to 1, with values closer to 1 representing higher income concentration. The MHDI is composed of well-established indicators to quantify three dimensions of human development: longevity, education and income; and it is adapted to the national context and uses local indicators available for the calculation. The MHDI ranges from 0 to 1, with values closer to 1 indicating higher human development.

Social Vulnerability Index (SVI) was obtained from the Institute of Applied Economic Research.² This index estimates the degree of vulnerability and social exclusion of a population and is composed of 16 social indicators comprising domains of urban infrastructure, human capital and income and work. The SVI scores range from 0 to 1, and higher values indicate higher social vulnerability.

Data analysis

We calculated the full scheme (second or single dose) immunisation rates (percentage) for each of the 5570 Brazilian municipalities. Crude rates were smoothed using the Local Empirical Bayesian Estimator. Spatial autocorrelation was measured using the Moran's Global Index and the Local Index of Spatial Association (LISA).³ Scattering diagrams were generated to position the municipalities into quadrants (Q) and calculated the neighbouring municipalities average into Q1 (high/high: positive values and positive averages), Q2 (low/low: negative values and negative averages); Q3 (high/low: positive values and negative averages); Q4 (low/high: negative values and positive averages).

Assumptions of normality were assessed by using the Kolmogorov–Smirnov test and homoscedasticity by the Levene test, and both children and adolescents’ vaccination rates showed a symmetrical distribution. Multiple linear regression models were fitted to relate the proportion of vaccinated people to the socio-economic indicators (Gini Index, SVI and MDHI). The analyses were performed in R, version 4.2.0, with a significance level of 5%.

Ethical considerations

Institutional review board approval and informed consent were not required because all data were obtained from public domain databases and were deidentified.

Results

Overall, 52.1% of children aged 5–11 years and 72.8% of adolescents aged 12–17 years have been fully vaccinated against COVID-19 in Brazil by mid-August 2022. COVID-19 vaccination rates for both children and adolescents’ groups varied across municipalities. There was spatial dependence on the smoothed rates for both children (I Moran 0.66; P < 0.001) and adolescent (I Moran 0.65; P < 0.001) groups. The highest rates of COVID-19 vaccination for both children and adolescent groups occurred in municipalities in the Southeast and South regions, whereas the lowest rates occurred in municipalities in the North and Northeast regions (Fig. 1 ). Municipalities with a higher Gini Index, higher SVI and lower MHDI were more likely to have a lower COVID-19 vaccination rate for both children and adolescents (Table 1 in Supplementary Material).

Fig. 1.

Spatial distribution of the percentage of children and adolescents fully vaccinated against COVID-19 in Brazil on August 16, 2022. (A) Local Empirical Bayesian Estimator and (B) Moran Map for the vaccination rate for children aged 5–11 years. (C) Local Empirical Bayesian Estimator and (D) Moran Map for the vaccination rate for adolescents aged 12–17 years.

Discussion

Although Brazil has a National Immunization Program (NIP) integrated to and based on primary healthcare facilities, with more than 35.000 vaccination rooms disseminated throughout the country,⁴ COVID-19 vaccination of children and adolescents was heterogeneously distributed, with spatial clusters of the lowest vaccination rates occurring mainly in municipalities with marked socio-economic disparities and social vulnerability, especially in the North and Northeast regions.

The World Health Organization global COVID-19 vaccination strategy targets 100% coverage for all older adults (aged ≥60 years), health workers and other priority risk groups with primary series and booster doses; and 70% of total population (irrespective of age group) for international benchmarking and against context-specific country targets.⁵ In Brazil, the Ministry of Health recommends a COVID-19 vaccination coverage of 90% of the population regardless of the age group for the complete primary schedule (dose 1 and dose 2 or single dose) and boosters.⁶ This study found a COVID-19 vaccination coverage of 52.1% for children aged 5–11 years and 72.8% for adolescents aged 12–17 years, both below the targets recommended. Furthermore, our findings highlighted a heterogeneous distribution of low coverage across the country.

The geographical distribution of lower COVID-19 vaccination coverage clusters resembles the distribution of cases and deaths among children and adolescents in Brazil.⁷ This shows that people living in socio-economically disadvantaged communities are substantially affected by COVID-19 not only in terms of incidence and mortality but also in vaccination access. In fact, people living in areas with large social inequalities often have difficult access to education and health services.

In addition, Brazil has suffered from misinformation campaigns about the COVID-19 vaccines,⁸ which would cause vaccine hesitation, especially among people with low access to scientifically based information. This demonstrates the need for awareness and information campaigns by official government agencies about the safety and efficacy of the COVID-19 vaccines for the paediatric populations.⁹

The southeast region had the highest COVID-19 vaccination coverage rates, especially the state of São Paulo. This may be related to two important aspects. São Paulo state concentrates on the municipalities with the highest MHDI in Brazil, with a well-structured health services network, providing greater opportunity for access to vaccination. In addition, COVID-19 vaccination in Brazil was started by São Paulo state by governmental initiative of importation and production of the adsorbed inactivated COVID-19 vaccine (Sinovac/Butantan), which later became part of the Brazilian NIP and after, also distributed to the other states.⁶

This study assessed a large sample size of children and adolescents fully vaccinated against COVID-19 and how social determinants of health are associated with lower COVID-19 vaccination rates in a country with marked social inequalities. Nevertheless, the results presented here need to be interpreted according to the study limitations. The secondary data and ecological studies are unsuitable to establish disease causality; and therefore, our analyses only provide evidence of statistically significant relationships between COVID-19 vaccination rates, poverty, and social inequalities. Also, our findings are only applied to children and adolescents aged 5–17 years.

Although low vaccination rates of children and adolescents occurred in all regions of Brazil, the main clusters of low COVID-19 vaccination occurred in municipalities in the North and Northeast, which are the regions with the worst socio-economic indicators and greatest health disparities. Identifying areas with lower vaccination coverage against COVID-19 may assist policymakers in the allocation of resources (as information campaigns and mass immunisation) to localities with the lowest vaccination rates for children and adolescents.

Author statements

Ethical approval

Institutional review board approval and informed consent were not required because all data were obtained from public domain databases and were deidentified.

Funding

There was no funding source for this study. The corresponding author has full access to all the data in the study and had final responsibility for the decision to submit for publication.

Competing interests

There is no conflict of interest.

Author contributions

V.S., T.S. and J.R.S. contributed to concept and design. All authors contributed to acquisition, analysis, or interpretation of the data; and critical revision of the article for important intellectual content. V.S. and T.S. drafted the article. J.R.S. contributed to statistical analysis. V.S. and J.R.S. contributed to administrative, technical, or material support. V.S. contributed to supervision.

Appendix A. Supplementary data

The following is the Supplementary data to this article: