ABSTRACT

Objective

To describe the polio vaccination status in 26 state capitals, the Federal District, and 12 municipalities in Brazil, among children born between 2017 and 2018.

Methods

This was a population-based household survey conducted from 2020 to 2022, which assessed polio vaccination coverage in children, considering valid, administered, and timely doses by municipality.

Results

Data were collected from 37,801 children. Vaccination coverage for the complete valid dose schedule was 87.5% (95%CI 86.2;88.7), dropping to 79.6% (95%CI 78.1;81.0), when the booster dose was considered. The dropout rate was 4.5% for the complete schedule, and 11.7% for the first booster. There was no correlation between campaign implementation and high coverage.

Conclusion

Vaccination coverage for the complete valid dose schedule and the first booster did not meet the 95.0% target. Regional disparities and the association between vaccination coverage and social indicators should be taken into consideration in strategies to increase coverage.

Palabras clave
Cobertura de Vacunación; Vacunas contra Poliovirus; Poliomielitis; Salud Infantil; Encuestas Epidemiológicas

Study contributions

Main results

Vaccination coverage for the complete poliomyelitis schedule was 87.5% (95%CI 86.2;88.7), with a reduction to 79.6% (95%CI 78.1;81.0) for the first booster dose. Dropout rate was 4.5% for the complete schedule, and 11.7% for the first booster dose.

Implications for services

Checking vaccination booklets helps identify and minimize factors associated with non-vaccination, which should be considered when defining effective strategies aimed at increasing vaccination coverage.

Perspectives

Understanding vaccination coverage guides the development of actions that support the improvement of vaccination coverage, consequently reducing the number of susceptible individuals and helping to control vaccine-preventable diseases.

Palabras clave
Cobertura de Vacunación; Vacunas contra Poliovirus; Poliomielitis; Salud Infantil; Encuestas Epidemiológicas

RESUMEN

Objetivo

Describir el estado vacunal contra la poliomielitis en 26 capitales estatales, Districto Federal y 12 municipios de Brasil, en niños nacidos en 2017-2018.

Métodos

Encuesta de hogares de 2020 a 2022, en la cual se evaluó la cobertura vacunal contra la poliomielitis, considerando doses válidas, aplicadas y oportunas por municipios.

Resultados

Se recogieron datos de 37.801 niños. La cobertura vacunal del esquema completo de dosis válidas fue 87,5% (IC95% 86,2;88,7), cayendo a 79,6% (IC95% 78,1;81,0), considerando el refuerzo de dosis. La tasa de abandono fue del 4,5% para la pauta completa y del 11,7% para el primer refuerzo. No hubo correlación entre realizar una campaña y una alta cobertura.

Conclusión

La cobertura de vacunación en esquema completo y en primer refuerzo no alcanzó la meta del 95,0%. Las diferencias regionales y la asociación de la cobertura vacunal con indicadores sociales deben considerarse en las estrategias para aumentarla.

Palabras clave
Cobertura de Vacunación; Vacunas contra Poliovirus; Poliomielitis; Salud Infantil; Encuestas Epidemiológicas

INTRODUCTION

Since 2016, vaccination coverage for vaccines included in the childhood vaccination schedule has been decreasing, reflecting the unsatisfactory result of this indicator for the polio vaccine in Brazil. In 2020, 2021 and 2022, national vaccination coverage for the complete schedule with first booster was 73.0%, 65.8% and 72.5%, respectively, falling short of the recommended target of 95.0%.¹1 SIPNI. Sistema de Informação do Programa Nacional de Imunizações (SI-PNI/CGPNI/DEIDT/SVS/MS). [citado em 5 de novembro de 2023]. Disponível em: http://tabnet.datasus.gov.br/cgi/dhdat.exe?bd_pni/cpnibr.def.
http://tabnet.datasus.gov.br/cgi/dhdat.e... These results may be associated with various factors, such as operational challenges, worsening socioeconomic conditions and vaccine hesitancy.²2 Barata RB, França AP, Guibu IA, et al. National Vaccine Coverage Survey 2020: methods and operational aspects. Rev Bras Epidemiol. 2023;26:e230031. The introduction of the polio vaccine in Brazil dates back to 1961.³3 Campos ALV, Nascimento DR, Maranhão E. A história da poliomielite no Brasil e seu controle por imunização. Hist Ciênc Saúde Manguinhos. 2003;10 Supl 2:573-600. In 2016, the use of the inactivated polio vaccine (IPV) was incorporated into the vaccination schedule, with three doses administered during the child’s first year of life (at 2, 4 and 6 months old), followed by two booster doses of the bivalent oral polio vaccine (bOPV),⁴4 Brasil. Ministério da Saúde. Secretaria de Vigilância em Saúde. Departamento de Vigilância das Doenças Transmissíveis. Coordenação Geral do Programa Nacional de Imunizações. NOTA TÉCNICA Nº 78/2016-CGPNI/DEVIT/SVS/MS. Vacinação contra poliomielite, mudanças no esquema vacinal e orientações aos serviços de saúde e usuários (rotina campanha e viajantes). Brasília: Ministério da Saúde: 2016 Abr. at 15 months and 4 years of age, as well as its administration during annual vaccination campaigns.⁵5 Brasil. Ministério da Saúde. Secretaria de Vigilância em Saúde. Coordenação Geral Do Programa Nacional de Imunizações. Plano Nacional de Resposta a um Evento de Detecção de Poliovírus e um Surto de Poliomielite: Estratégia do Brasil. Brasília-DF: Ministério da Saúde; 2022 Abr. However, the aforementioned vaccination schedule will undergo changes in 2024, as the World Health Organization (WHO) recommends the use of IPV whenever possible ,⁶6 WHO. Standard operating procedures: responding to a poliovirus event or outbreak, version 4. Geneva: World Health Organization; 2022. and, therefore, booster doses will be administered with IPV rather than bOPV.⁵5 Brasil. Ministério da Saúde. Secretaria de Vigilância em Saúde. Coordenação Geral Do Programa Nacional de Imunizações. Plano Nacional de Resposta a um Evento de Detecção de Poliovírus e um Surto de Poliomielite: Estratégia do Brasil. Brasília-DF: Ministério da Saúde; 2022 Abr.,⁷7 Brasil. Ministério da Saúde. Governo anuncia atualização da vacina contra a pólio a partir de 2024: reforço será feito com vacina injetável, após período de transição, e representa avanço tecnológico. Publicado em 07 de julho de 2023a. Disponível em: https://www.gov.br/pt-br/noticias/saude-e-vigilancia-sanitaria/2023/07/governo-anuncia-atualizacao-da-vacina-contra-a-polio-a-partir-de-2024.
https://www.gov.br/pt-br/noticias/saude-...

It is worth highlighting that poliomyelitis is an acute viral infectious disease primarily affecting children under 5 years of age, and in 1% of cases, the disease causes sudden onset of asymmetric flaccid paralysis in the lower limbs, with preserved sensation, and areflexia in the affected region.⁸8 BRASIL. Ministério da Saúde, Secretaria de Vigilância em Saúde, Coordenação-Geral de Desenvolvimento da Epidemiologia em Serviços. Guia de Vigilância em Saúde: volume único. 4ª edição. Brasília: Ministério da Saúde; 2019. Transmission occurs most frequently through direct contact with feces or secretions from the mouth of sick people or carriers.⁸8 BRASIL. Ministério da Saúde, Secretaria de Vigilância em Saúde, Coordenação-Geral de Desenvolvimento da Epidemiologia em Serviços. Guia de Vigilância em Saúde: volume único. 4ª edição. Brasília: Ministério da Saúde; 2019.,⁹9 Brasil. Ministério da Saúde. Secretaria de Vigilância em Saúde. Departamento de Articulação Estratégica de Vigilância em Saúde. Guia de Vigilância em Saúde. 5ª edição rev. atual. Brasília: Ministério da Saúde; 2022. Motor deficits often progresses within three days, with 5% to 10% of cases resulting in death due to respiratory muscle paralysis, and ¹⁰10 Centers for Disease Control and Prevention – CDC. What is Polio? Set. 2021. Disponível em: https://www.cdc.gov/polio/index.htm. [consultado em 26 de outubro de 2021].
https://www.cdc.gov/polio/index.htm. [co... and one in every 200 infections leads to irreversible paralysis.⁸8 BRASIL. Ministério da Saúde, Secretaria de Vigilância em Saúde, Coordenação-Geral de Desenvolvimento da Epidemiologia em Serviços. Guia de Vigilância em Saúde: volume único. 4ª edição. Brasília: Ministério da Saúde; 2019.

It is worth noting that in 1988, the 41^st World Health Assembly adopted a resolution for the global eradication of poliomyelitis, which led to the creation of the Global Polio Eradication Initiative (GPEI).¹¹11 World Health Organization – WHO. Global Polio Eradication Initiative. Polio Endgame Strategy 2019-2023: Eradication, integration, certification and containment. Geneva: World Health Organization; 2019. This initiative enhanced the capacity to combat other infectious diseases and to improved surveillance and immunization efforts,¹²12 Organização Pan-Americana de Saúde - OPAS. Poliomielite. Jan. 2021. Disponível em: https://www.paho.org/pt/topicos/poliomielite.
https://www.paho.org/pt/topicos/poliomie... which contributed to the reduction of cases, given that currently 80% of the world’s population lives in regions certified as polio-free.¹³13 Zaffran M, MsGovern M, Hossaini R, Martin R, Wenger j. The polio endgame: securing a world free of all polioviruses. Lancet. 2018;91(10115):11-3.

Brazil was certified as polio-free in 1994; however, there is a risk of imported cases,¹⁴14 BRASIL. Ministério da Saúde. Poliomielite. Nov. 2020. Disponível em: https://www.gov.br/saude/pt-br/assuntos/saude-de-a-a-z/p/poliomielite. [consultado em 26 de outubro de 2023].
https://www.gov.br/saude/pt-br/assuntos/... as there are countries with endemic transmission, such as Afghanistan and Pakistan.¹⁵15 Global Polio Eradication Initiative - GPEI. Endemic Countries [Internet]. 2021. Disponível em: https://polioeradication.org/where-we-work/polio-endemic-countries/. [consultado em 25 de outubro de 2023].
https://polioeradication.org/where-we-wo... ,¹⁶16 Global Polio Eradication Initiative - GPEI. Public Health Emergency status [Internet]. 2023. Disponível em: https://polioeradication.org/polio-today/polio-now/public-health-emergency-status/. [consultado em 5 de novembro de 2023].
https://polioeradication.org/polio-today... Nevertheless, over 25 countries have detected cases of wild poliovirus type 1 or vaccine-derived poliovirus, posing a potential risk of international spread.¹⁶16 Global Polio Eradication Initiative - GPEI. Public Health Emergency status [Internet]. 2023. Disponível em: https://polioeradication.org/polio-today/polio-now/public-health-emergency-status/. [consultado em 5 de novembro de 2023].
https://polioeradication.org/polio-today... It is noteworthy that, as long as there is an infected child, susceptible children in all countries are at risk of contracting poliomyelitis,¹⁵15 Global Polio Eradication Initiative - GPEI. Endemic Countries [Internet]. 2021. Disponível em: https://polioeradication.org/where-we-work/polio-endemic-countries/. [consultado em 25 de outubro de 2023].
https://polioeradication.org/where-we-wo... highlighting the need to maintain high vaccination coverage,⁹9 Brasil. Ministério da Saúde. Secretaria de Vigilância em Saúde. Departamento de Articulação Estratégica de Vigilância em Saúde. Guia de Vigilância em Saúde. 5ª edição rev. atual. Brasília: Ministério da Saúde; 2022.,¹¹11 World Health Organization – WHO. Global Polio Eradication Initiative. Polio Endgame Strategy 2019-2023: Eradication, integration, certification and containment. Geneva: World Health Organization; 2019. a fact that underscores the importance of conducting studies that help understand the vaccination situation and guide actions to achieve better results.

The objective of this study was to describe the polio vaccination status in 26 state capitals, the Federal District and 12 municipalities in Brazil, in children born in 2017 and 2018.

METHODS

This was a population-based household survey, conducted from a cohort of live-born children in 2017 and 2018, residing in the urban area of the 26 state capitals, the Federal District and 12 municipalities with over 100,000 inhabitants, namely: Campinas/São Paulo state, Caruaru/Pernambuco state, Imperatriz/Maranhão state, Joinville/Santa Catarina state, Londrina/Paraná state, Petrópolis/Rio de Janeiro state, Rio Grande/Rio Grande do Sul state, Rio Verde/Goiás state, Rondonópolis/Mato Grosso state, Sete Lagoas/Minas Gerais state, Sobral/Bahia state and Vitória da Conquista/Bahia state.²2 Barata RB, França AP, Guibu IA, et al. National Vaccine Coverage Survey 2020: methods and operational aspects. Rev Bras Epidemiol. 2023;26:e230031.

Data collection

Data collection was carried out between September 2020 and March 2022, taking into account the social distancing periods implemented in each location. Data on the dates of administration of each vaccine during the first 24 months of life, were obtained considering the vaccines administered routinely, in both public and private services, a well as those administered during campaigns.

The vaccination booklets were photographed, read and transcribed into the research database by nurses with experience in the activities of the National Immunization Program (Programa Nacional de Imunizações - PNI). Those booklets not found in the household were retrieved from the PNI Information System (Sistema de Informação do PNI - SI-PNI). In addition, a structured questionnaire was administered, containing closed-ended questions related to the sociodemographic data of the child; the reproductive and sociodemographic data of the mother; household and family consumption information; and the child’s vaccination data. More details on the data collection instrument and field strategies are described in the methodological reference article.²2 Barata RB, França AP, Guibu IA, et al. National Vaccine Coverage Survey 2020: methods and operational aspects. Rev Bras Epidemiol. 2023;26:e230031.

Sampling

The sample design considered separate surveys for each city. Thus, the following were considered for the calculation: a hypothetical population of 1 million live births; estimated prevalence of vaccination coverage = 70%, margin of error = 5%; z = 1.96 for a 95% confidence interval (95% CI); and a design effect of 1.4, resulting in a total of 452 children per survey.

Depending on the population size of live births, between one and four surveys were conducted per municipality, with only one survey being conducted in 15 cities (four capitals and 11 inland cities), two surveys in nine capitals, three surveys in four capitals and four surveys in nine capitals, he Federal District and one inland city.

The sampling procedure begins with the definition of socioeconomic strata created through cluster analysis, based on socioeconomic indicators (average income of household heads, proportion of literate heads of household and proportion of heads of household with income greater than or equal to 20 minimum wages) from the urban census tracts of each city, according to data from the 2010 Demographic Census.

The cluster analysis generated four strata (A to D) of census tracts with distinct socioeconomic characteristics. Stratum A is related to high-income socioeconomic groups; B, upper-middle income; C, lower-middle income; and D, low-income.² Children from the cohorts of interest living in each tract were estimated through georeferencing of addresses contained in the Live Birth Information System (Sistema de Informação sobre Nascidos Vivos - SINASC) and projections based on the distribution observed in the 2010 Census.

The sectors were grouped by proximity (clusters) and expected number of children, so that each cluster contained three times the number of children to be included in the sample. The clusters were systematically selected to cover the entire geographic area. Using maps of the clusters and the list of addresses obtained from SINASC, the interviewers covered the area identifying children from the cohorts until the pre-established number was reached for each stratum in each city, as described in the methodological article of the study.²2 Barata RB, França AP, Guibu IA, et al. National Vaccine Coverage Survey 2020: methods and operational aspects. Rev Bras Epidemiol. 2023;26:e230031.

Indicators and data analysis

To calculate vaccination coverage, the number of live births registered in SINASC in 2017 and 2018 was used as the denominator; for numerators, different criteria were applied to consider doses administered (dose administered regardless of timing) , valid doses (dose administered considering the timing, in relation to the child’s date of birth, and observing the interval between doses) and timely (doses recommended according to the vaccination schedule, taking into account the minimum and maximum ages for each vaccine and adequate intervals between doses),¹⁷17 Tauil MC, Sato APS, Costa AA, Inenami M, Ferreira VLR, Waldman EA. Coberturas vacinais por doses recebidas e oportunas com base em um registro informatizado de imunização, Araraquara-SP, Brasil, 2012-2014. Epidemiol. Serv. Saúde [Internet]. 2017 Dez;26(4):835-846. [citado em 24 de fevereiro de 2024]. Disponível em: http://scielo.iec.gov.br/scielo.php?script=sci_arttext&pid=S1679-49742017000400835&lng=pt detailed below:

• Vaccination coverage at 12 months

  • Doses administered

    • Dose 1: combination of the first dose of IPV + hexavalent vaccine (acellular pertussis, IPV, hepatitis B and Haemophilus influenzae type B) + acellular (acellular pertussis and IPV);

    • Dose 2: combination of the second dose of IPV + hexavalent vaccine + acellular vaccine;

    • Dose 3: combination of the third dose of IPV + hexavalent vaccine + acellular vaccine.

  • Valid doses

    • Dose 1: first dose administered at 42 days or older

    • Dose 2: second dose administered at least 30 days after the first dose;

    • Dose 3: third dose administered at least 30 days after the second dose.

  • Timely doses

    • Dose 1: first dose administered between 42 and 89 days;

    • Dose 2: second dose administered between 70 and 151 days;

    • Dose 3: third dose administered between 98 and 212 days.

• Vaccination coverage considering the first booster dose

  • Doses administered

    • Dose 1: combination of the first dose of OPV + fourth dose of IPV administered ≥ 12 months.

  • Valid doses of OPV

    • Dose 1: first dose administered at 365 days or more after having received the previous three IPV doses.

  • Timely doses of OPV

    • Dose 1: first dose administered between 365 and 486 days, having received the previous three IPV doses.

The following were also considered:

• Dropout rate indicator for complete IPV vaccination schedule: difference between dose 1 IPV administered and dose 3 IPV administered/dose 1 IPV administered*100.

• Dropout rate indicator for booster dose: difference between dose 1 IPV administered and dose 1 OPV (first booster)/ dose 1 IPV administered*100.

Vaccination coverage indicators were analyzed in general, considering the different dose criteria. Valid dose indicators were used to analyze coverage behavior among capitals and municipalities, which was also used in the preliminary investigation of the association between polio vaccination coverage and socioeconomic and demographic factors.

In order to analyze vaccination coverage, five groups were also established: satisfactory (equal to or greater than 95%); reasonable (90% to 94.9%); unsatisfactory (80% to 89.9%); critical (70% to 79.9%); and very critical (equal to or less than 69.9%). These groups were established based on the understanding that satisfactory coverage corresponds to the recommended target of 95%,¹⁸18 Pan American Health Organization. Final of the XV Meeting of the Technical Advisory Group on Vaccine preventable Diseases – Municipalities: improving immunization services. Washington: PAHO; 2002. Disponível em: https://www.paho.org/en/documents/final-report-xv-meeting-technical-advisory-group-vaccinepreventable-diseases
https://www.paho.org/en/documents/final-... and the other groups below this, so that, as the values move away from the recommended target, the greater the efforts of the municipality to reach the target, and the larger the susceptible population; consequently, the greater the risk of disease and transmission.

As the sample was stratified and clustered by census sector with disproportionate allocation, it was necessary to calculate and apply sample weights to each household interviewed for estimates. The analyses were performed by applying the definitions of weights, strata and clusters to calculate the estimates of vaccination coverage and their respective 95% confidence intervals, as well as correlations between coverage, first booster schedule and vaccination campaigns were analyzed by means of Spearman’s correlation test, using SPSS version 22.

Ethical aspects

The research was approved by the Research Ethics Committees of the Instituto de Saúde Coletiva da Universidade Federal da Bahia, under opinion No. 3,366,818, on June 4, 2019, with Certificate of Submission for Ethical Appraisal (CAAE) 4306919.5.0000.5030; and of the Irmandade da Santa Casa de São Paulo, under opinion No. 4,380,019, on November 4, 2020, with CAAE 39412020.0.0000.5479.

RESULTS

The final sample consisted of 37,801 live births, after a loss corresponding to 6% of the total sample in each municipality. Thus, it was observed that vaccination coverage based on doses administered for IPV (complete schedule) was 88.0% (95%CI 86.7;89.1) and for OPV it was 81.2% (95%CI 79.8;86.7) (first booster dose) both of which are below the 95.0% expected by the Ministry of Health (Table 1).

This result indicates a 6.8 percentage point difference between the completion of the vaccination schedule and the first booster dose, recommended at 15 months old. It is noteworthy that the dropout rate for the complete IPV schedule based on doses administered was 4.5%, lower than the dropout rate related to the vaccination schedule with the first booster dose (11.7 %) (Table 1).

When criteria for considering valid doses were established, there was a reduction in coverage for the complete IPV schedule (87.5%; 95%CI 86.2;88.7) and OPV (79.6%; 95%CI 78.1;81.0). This result highlights a greater reduction in valid and timely dose coverage for OPV doses compared to the coverage of these doses for the schedule with IPV doses. For 1.7% of the children who received OPV, the doses administered were not considered valid, while for 0.6%, the third doses of IPV administered were not considered valid (Table 1).

When vaccination coverage was analyzed based on timeliness, there was a greater reduction than when coverage was based on administered and valid doses, both for IPV (58.3%; 95%CI 56.5;60.1) and for OPV (41.6%; 95%CI 39.9;43.2). It is found that, among the doses administered, 38.9% of the third doses of IPV were not administered between 98 and 212 days after the second dose of IPV, and that 51.1% of the first booster doses with OPV were administered between 365 and 486 days after completion of the IPV schedule (Table 1).

Regarding vaccination coverage of the first booster, the target was not reached in any of the cities analyzed, with the highest coverage being 93.3% (95%CI 90.7;95.2) in Joinville/Santa Catarina state, and the lowest being 61% (95%CI 57.3;67.9) in Florianópolis/Santa Catarina state (Table 2). From this perspective, considering the established groups, a concentration of 10.3% of the municipalities was observed in the reasonable group, with vaccination coverage ranging from 90.5% to 93.3%. In the unsatisfactory group, 53.8% of the municipalities were concentrated with coverage ranging from 80% to 89.1%; in the critical group, coverage ranged from 70.9% to 79.8%, accounting for 30.8% of the municipalities. Finally, in the very critical group , 5.1% of municipalities with coverage ranging from 61.0% (95%CI 53.7;67.9) to 62.2% (95%CI 54.3;69.5), were observed (Table 2).

Vaccination coverage for booster doses in the 12 large urban centers (São Paulo/São Paulo state, Brasília/Federal District, Rio de Janeiro/Rio de Janeiro state, Manaus/Amazonas state, Belém/Pará state, Fortaleza/Ceará state, Recife/Pernambuco state, Salvador/Bahia state, Belo Horizonte/Minas Gerais state, Curitiba/Paraná state, Goiânia/Goiás state and Porto Alegre/Rio Grande do Sul state) ranged from 71.5% (95%CI 62.7;78.9) to 88.4% (95%CI 83.9;91.8), with a higher concentration of these centers in the critical group (Table 2).

It was not possible to observe high coverage of campaign doses (Table 2), and the data show that, after performing the statistical test, there was no correlation between conducting campaigns and high vaccination coverage.

When socioeconomic strata were observed, none achieved the recommended vaccination coverage; stratum C showed the best coverage for valid IPV doses (89.1%; 95%CI 87.4;90.7); however, stratum D presented better coverage for the vaccination schedule with the first booster (84.8%; 95%CI 83.0;86.4), higher than stratum A [complete schedule – 79.1% (95%CI 74.2;83.2) and with first booster – 64.7% (95%CI 60.0;69.2)]. Furthermore, it is inferred that booster dose coverage varied more between strata [64.7% (95%CI 60.0;69.2) to 84.8% (95%CI 83.0;86.4)] than IPV coverage [79.1% (95%CI 74.2;83.2) to 89.1% (95%CI 87.4;90.7)] (Table 3).

In this context, when analyzing the characteristics of the family, mother and child, it can be inferred that, for the complete IPV schedule, when considering the confidence intervals, vaccination coverage for strata according to consumer goods C (89.1%; 95%CI 87.3;90.7) and D (88.2%; 95%CI 86.4;89.7) is higher than for stratum B (87.3%; 95%CI 84.6;89.6), which, in turn, is higher than stratum A (81.8%; 95%CI 75.7;86.7). It is noted that vaccination coverage for those who receive the Bolsa Família Program benefit (90.9%; 95%CI 89.3;92.3) is higher than for those who do not receive it (86.3%; 95%CI 84.8;87.7) (Table 4).

It is noteworthy that the vaccination coverage of the group in where mothers work (90.2%; 95%CI 88.7;91.4) is higher than that of mothers who do not work (86.0%; 95%CI 84.0;87.7), a pattern also observed for the complete vaccination schedule with the first booster dose, in which there are, respectively, 84.5% (95%CI 82.8;86.1) and 76.0% (95%CI 73.9;78.0) (Table 4).

Regarding the analysis focused on the complete schedule with the first booster dose, it is found that White race/skin color has lower coverage (75.1%; 95%CI 72.6;77.5) compared to Black (87.9%; 95%CI 85.3;90.1) and mixed-race (83.1%; 95%CI 81.4;84.7). In addition, vaccination coverage for consumer goods strata C (85.7%; 95%CI 83.6;87.5) and D (85.0%; 95%CI 83.3;86.7) is higher than that for stratum B (69.8%; 95%CI 66.3;73.0), which in turn is higher than that for stratum A (43.3%; 95%CI 36.2;50.8); as observed with the complete vaccination schedule, it is also found that vaccination coverage for those receiving the Bolsa Família Program benefit (86.8%; 95%CI 85.2;88.2) is higher than for those who do not receive it (77.1%; 95%CI 75.3;78.8) (Table 4).

For the first booster, vaccination coverage is lower for mothers aged 35 or over (74.9%; 95%CI 72.2;77.5). In addition, it was observed that, for mothers without a partner, vaccination coverage is more satisfactory (84.0%; 95%CI 81.7;86.0), compared to those with a partner (78.6%; 95%CI 76.8;80.2). Nevertheless, mothers with 16 years of education or more vaccinate their children less, with coverage of 69.6% (95%CI 66.6;72.4) for this group (Table 4).

It is noteworthy that, for vaccination with a booster dose, the analysis of monthly household income shows that coverage is higher in the group of families with income between BRL1,001.00 to BRL3,000.00 (86.2%; 95%CI 84.2;88.0), which in turn is higher than that of the groups from BRL3,001.00 to BRL8,000.00 (80.9%; 95%CI 77.6;83.8) and BRL8,001.00 or more (61.2%; 95%CI 56.1;66.1). There is also higher coverage in the group that does not use private services (84.8%; 95%CI 83.5;86.0), i.e., those who receive vaccination through the Brazilian National Health System (Sistema Único de Saúde - SUS) (Table 4).

DISCUSSION

This study showed that the estimated coverage for IPV and OPV did not meet the recommended target, with no homogeneity observed in the coverage analyzed,¹⁹19 Bechini A, Boccalini S, Ninci A, Zanobini P, Sartor G, Bonaccorsi G, et al. Childhood vaccination coverage in Europe: impact of different public health policies. Expert Rev Vaccines. 2019 Jul;18(7):693-701. with lower coverage with booster doses, with a significant reduction in vaccination coverage when considering validity and timeliness.

Regarding the observed OPV vaccination coverage, which was higher than that measured in the SI-PNI,¹1 SIPNI. Sistema de Informação do Programa Nacional de Imunizações (SI-PNI/CGPNI/DEIDT/SVS/MS). [citado em 5 de novembro de 2023]. Disponível em: http://tabnet.datasus.gov.br/cgi/dhdat.exe?bd_pni/cpnibr.def.
http://tabnet.datasus.gov.br/cgi/dhdat.e... it is worth highlighting that this result may be directly associated with the data collection method, since checking physical records addresses issues related to the recording of doses administered in the information system, potentially leading to differences between local data and consolidated national figures.²⁰20 Domingues CMAS, Maranhão AGK, Teixeira AM, Fantinato FFS, Domingues RAS. 46 anos do Programa Nacional de Imunizações: uma história repleta de conquistas e desafios a serem superados. Cad Saúde Pública [Internet]. 2020;36 Suppl 2.

Although no significant differences were observed between socioeconomic strata A, C, and D, where wealthier individuals tend to vaccinate less, a fact also observed in other studies,²¹21 Gilbert NL, Gilmour H, Wilson SE, Cantin L. Determinants of non-vaccination and incomplete vaccination in Canadian toddlers. Hum Vaccin. Immunother. 2017;13(6):1-7. it is worth noting that there is a greater possibility of international exposure among wealthier individuals, which could increase the likelihood of infection and the importation of cases, as described in a study on the introduction of COVID-19 in Brazil.²² However, in the face of local transmission, it is understood that, even with more satisfactory coverage among poorer populations, given the existing social conditions and determinants, this population may be more affected, as observed in the COVID-19 pandemic.²²22 Martin PS, Gonçalves SL, Goularte PS, Dias EP, Leonardi AE, Tiezzi DG, et al. História e Epidemiologia da COVID-19. ULAKES JOURNAL OF MEDICINE [Internet]. 2020 Jul 20;1. Disponível em: https://revistas.unilago.edu.br/index.php/ulakes/article/view/253/232.
https://revistas.unilago.edu.br/index.ph... ,²³23 Barreto ML. Esboços para um cenário das condições de saúde da população brasileira 2022/2030. In: Fundação Oswaldo Cruz. A saúde no Brasil em 2030 - prospecção estratégica do sistema de saúde brasileiro: população e perfil sanitário [online]. Rio de Janeiro: Fiocruz/Ipea/Ministério da Saúde/Secretaria de Assuntos Estratégicos da Presidência da República; 2013;2:97-120.

It is worth highlighting that family, maternal and child characteristics, when analyzed in a univariate manner, only allow for inferences, and it could be seen that the results focused on the vaccination schedule with the first booster dose being more satisfactory in the group with lower-income families may be linked to those who are beneficiaries of the Bolsa Família Program, which also use the SUS for vaccination, which is a requirement of the program itself,²⁴24 Brasil. Ministério do Desenvolvimento e Assistência Social, Família e Combate à Fome. Cartilha do Programa Bolsa Família. 2023. and this initiative can be a key factor in achieving vaccination coverage in Brazil. A study conducted in Brazil and its regions in 2018 shows that the Bolsa Família Program contributed to increasing overall vaccination status among children.²⁵25 Kern AP, Vieira M, Freguglia R. Impactos do programa bolsa família na imunização das crianças. 46º Encontro Nacional de Economia. Anais do 46º Encontro Nacional de Economia. Rio de Janeiro, Brasil; 2018:1-20.

However, considering the immunity conferred by booster doses,²⁶26 Global Polio Eradication Iniciative - GPEI Fact Sheet: Vaccine-Derived Poliovirus [Internet]. 2019. Disponível em: https://polioeradication.org/wp-content/uploads/2018/07/GPEI-cVDPV-Fact-Sheet-20191115.pdf. [consultado em 4 de novembro de 2023].
https://polioeradication.org/wp-content/... it is crucial to emphasize the importance of a complete vaccination schedule with all recommended doses. Taking into account additional risk factors, such as population density, intermunicipal and interstate flow, migration flows, and the presence of important gateways (ports, airports and bus stations),²⁷27 IBGE. Instituto Brasileiro de Geografia e Estatística. IBGE mostra a nova dinâmica da rede urbana brasileira: Existem no país doze grandes redes de influência, que interligam até mesmo municípios situados em diferentes estados [Internet]. Publicado em 10 de outubro de 2008. underscore the need to increase vaccination coverage in large urban centers.

Furthermore, some states, such as Acre, Amazonas, Goiás, Mato Grosso, Mato Grosso do Sul, Rio Grande do Sul and Paraná, have native populations living in hard-to-reach areas and border populations, making them more vulnerable⁵5 Brasil. Ministério da Saúde. Secretaria de Vigilância em Saúde. Coordenação Geral Do Programa Nacional de Imunizações. Plano Nacional de Resposta a um Evento de Detecção de Poliovírus e um Surto de Poliomielite: Estratégia do Brasil. Brasília-DF: Ministério da Saúde; 2022 Abr. and requiring specific strategies to reach these populations.

In this context, the study showed the importance of checking physical vaccination booklets, since they are the primary tool for vaccination verification, in addition to facilitating the understanding of vaccination coverage, they also assist in the process of defining effective strategies to minimize barriers to vaccination.²⁸28 Fonseca KR, Buenafuente SMF. Análise das coberturas vacinais de crianças menores de um ano em Roraima, 2013-2017. Epidemiol Serv Saúde. 2021;30(2). These strategies must consider existing regional differences and the needs of the most vulnerable populations, and that, in addition to adherence to vaccination, it can be promoted in a timely manner, in order to reduce the number of susceptible people in a given period.

Efforts to minimize vaccine hesitancy are crucial for reducing dropout rates in both complete vaccination schedules and booster doses, given that the WHO has included it in the list of top ten threats to global health, given its potential to reverse progress in combating vaccine-preventable diseases. ²⁸28 Fonseca KR, Buenafuente SMF. Análise das coberturas vacinais de crianças menores de um ano em Roraima, 2013-2017. Epidemiol Serv Saúde. 2021;30(2).,²⁹29 World Health Organization. Ten threats to global health in 2019. Geneva: World Health Organization [Internet]. 2019. Thus, vaccine hesitancy poses a challenge to improving vaccination coverage, one that extends beyond access issues, since this study shows that, for polio coverage, vaccination campaigns were not correlated with high coverage, highlighting the need to assess communication and public engagement strategies, aimed to obtain satisfactory results, similar to those historically attained by the PNI.³⁰30 Nascimento DR. As campanhas de vacinação contra a poliomielite no Brasil (1960-1990). Ciênc. Saúde Colet. 2011;16(2):501-11.

The limitations of this survey are related to access to families – due to mistrust, urban insecurity or lack of interest in participating in surveys –, as well as difficulty in reading vaccination booklets and the fact that the census was not conducted in 2020, which led to the use of outdated data to define socioeconomic strata, which may have generated selection bias.²2 Barata RB, França AP, Guibu IA, et al. National Vaccine Coverage Survey 2020: methods and operational aspects. Rev Bras Epidemiol. 2023;26:e230031.

In conclusion, understanding the vaccination status guides decision-making processes in the development of actions to increase vaccination coverage and redefine strategies, such as campaigns. This, in turn, is expected to reduce the number of susceptible individuals, helping control vaccine-preventable diseases and reducing the risk of reintroducing diseases that have been eliminated in certain regions.

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