Persistence of immunity against hepatitis A in Brazilian children vaccinated with a single dose of inactivated virus vaccine.

In 2014, the Brazilian National Immunization Program implemented the universal vaccination against the hepatitis A virus (HAV) for children aged 12 months and older, applying a single dose of the inactivated virus vaccine. It is essential to carry out follow-up studies in this population, aiming to verify the longevity of HAV immunological memory. This study evaluated the humoral and cellular immune response of a cohort of children vaccinated between 2014 and 2015, and further investigated between 2015 and 2016, and who had their initial antibody response assessed after the single dose. A second evaluation took place in January 2022. We examined 109 children out of the 252 that took part in the initial cohort. Seventy (64.2%) of them had anti-HAV IgG antibodies. Cellular immune response assays were performed in 37 anti-HAV-negative and 30 anti-HAV-positive children. Production of interferon-gamma (IFN-y) stimulated with the VP1 antigen was demonstrated in 34.3% of these 67 samples. Of the 37 negative anti-HAV samples, 12 (32.4%) produced IFN-y. Among the 30 anti-HAV-positive, 11 (36.7%) produced IFN-y. In total, 82 (76.6%) children presented some type of immune response against HAV. These findings demonstrate the persistence of immunological memory against HAV in the majority of children vaccinated between 6 and 7 years with a single dose of the inactivated virus vaccine.

Impact of the single-dose universal mass vaccination strategy against hepatitis A in Brazil.

Universal vaccination of children against hepatitis A was introduced in 2014 in Brazil as a single-dose schedule. We analyzed the numbers of reported cases of hepatitis A virus infection (HAV) from 2010 to 2017 to evaluate the initial impact of that intervention. Data were assessed and has been freely available on the Brazilian Ministry of Health website. The HAV incidence was steady around 6000 cases per year until 2014. Between 2014 and 2016, there was a 85.5% cumulative drop, independent of gender and geographical macroregions. The fall was especially significant among toddlers (96.8%). In 2017, cases increased due to an outbreak among male adults in São Paulo. Decrease in incidence continued to occur for females and for those under 15 years of age. Data show that there was a significant decrease in HAV cases number in Brazil from 2015 after the introduction of single-dose HAV vaccine program.