Adolescents who received hepatitis B virus (HBV) vaccinations as infants still showed protection despite little evidence of residual antibodies, a study showed.

This finding was based on data from a prospective study of 137 children, aged 10-11 years, and 213 children, aged 15-16 years, with no history of HBV infection who were vaccinated at 2, 4, and 6 months of age. Michelle Pinto, MD , of the Vaccine Evaluation Center in Vancouver and her colleagues measured residual immunity to determine whether HBV boosters might be needed in adolescents vaccinated as infants to prolong immunity and reduce disease transmission in adulthood.

Overall, 97% of the younger age group and 91% of the older age group showed reactions to an HBV vaccine challenge. An additional 3 (2%) younger children and 12 (6%) older children responded to a second vaccine challenge after failing to respond to the first.

Limitations of the study included a “limited ability of the challenge vaccine procedure to accurately identify immune memory and anamnestic responses” and the differences between the findings and those from long-term outcome data in similar studies in other countries, Dr. Pinto and her associates wrote.

However, “the fact that substantial differences exist in measures of residual protection among teenagers after infant or adolescent HBV vaccinations warrants close ongoing scrutiny of whether important differences will emerge in long-term protection, with or without booster vaccination,” they said (Pediatr Infect Dis J. 2017. doi: 10.1097/INF.0000000000001543 ).