Revista do Instituto de Medicina Tropical de São Paulo · 5 authors, 3 centres
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In a Brazilian cohort of 825 children, MMR and hepatitis A vaccine adherence was below the 95% target (90.6% and 74.9%, respectively). Factors such as white maternal skin color, paid maternity leave, multiparity, fewer antenatal visits, and childcare attendance were linked to incomplete vaccination; vitamin A deficiency was associated with seronegativity for mumps. These findings highlight the need for targeted public health strategies to improve vaccine uptake and immune response.
**Background:** Vaccination coverage has been declining in Brazil and globally, raising concerns about the resurgence of vaccine-preventable diseases. Immune responses after vaccination are not uniform and may be influenced by sociodemographic and nutritional factors. This study aimed to assess adherence to MMR and hepatitis A vaccines and identify factors associated with incomplete vaccination and seronegative antibody results among 2-year-old children in the MINA-BRAZIL cohort.
**Methods:** This population-based cohort included 825 children born between July 2015 and June 2016 in Cruzeiro do Sul, Acre, Brazil. Vaccination data were obtained from official immunization cards. Blood samples were collected at the 2-year follow-up visit and analyzed using commercial ELISA kits for measles (Euroimmun), mumps (R-Biopharm), and hepatitis A (Dia.Pro). Incomplete vaccination was defined as failure to receive two doses of MMR (or one MMR + one MMRV) or a single dose of hepatitis A vaccine. Seronegativity was defined using manufacturer cutoffs (measles: <200 UI/L; mumps: <14 UI/mL; hepatitis A: <NC+PC/3). Modified Poisson regression with robust variance was used to estimate risk ratios, with variables selected via a hierarchical approach.
**Key Results:** Among 825 children, adherence was 90.6% for MMR, 76.7% for MMRV, and 74.9% for hepatitis A. In multivariable models, factors associated with incomplete MMR vaccination included: white maternal skin color (aRR 0.66, 95% CI 0.50–0.87, p=0.005), paid maternity leave (aRR 1.35, 95% CI 1.06–1.72, p=0.016), multiparity (aRR 0.61, 95% CI 0.47–0.80, p<0.001), fewer than 6 antenatal visits (aRR 0.61, 95% CI 0.47–0.78, p<0.001), and childcare attendance (aRR 1.87, 95% CI 1.19–2.96, p=0.007). For hepatitis A, white maternal skin color (aRR 0.71, 95% CI 0.52–0.96, p=0.027) and not having a cohabiting partner (aRR 0.67, 95% CI 0.52–0.87, p=0.002) were associated with incomplete vaccination. Among vaccinated children, seropositivity was 86.9% for measles (2 doses), 74.9% for mumps (2 doses), and 83.6% for hepatitis A. Receiving Bolsa Familia allowance was associated with seronegativity for measles (aRR 1.70, 95% CI 1.14–2.55, p=0.010) and mumps (aRR 1.35, 95% CI 1.01–1.81, p=0.045). Two vaccine doses reduced the risk of measles seronegativity by 36% (aRR 0.64, 95% CI 0.41–1.00, p=0.048). Vitamin A deficiency was associated with mumps seronegativity (aRR 1.39, 95% CI 1.05–1.85, p=0.023). No significant associations were found for hepatitis A seronegativity.
**Clinical Implications:** MMR and hepatitis A vaccine coverage in this Brazilian cohort fell short of the 95% target, with social determinants—including maternal skin color, paid leave, multiparity, antenatal care, and childcare attendance—playing a significant role in incomplete vaccination. Vitamin A deficiency was linked to reduced mumps antibody response, suggesting that nutritional interventions may improve vaccine immunogenicity. These findings underscore the need for targeted public health strategies, including improved communication, expanded access to primary care, and nutritional support, to enhance vaccine uptake and effectiveness in vulnerable populations.