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

Abstract

AbstractIn 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.