Immunogenicity of an inactivated hepatitis A vaccine in infants and young children.

Background: Infants with passively transferred maternal antibody, born to mothers immune to hepatitis A virus (HAV), have a blunted response to hepatitis A (HA) vaccine. We compared HA vaccine immunogenicity among infants born to immune and susceptible mothers, vaccinated on different schedules. Methods: Infants were randomized into 3 groups, each receiving 2 doses of 720 EL.U. of HA vaccine (HAVRIX; Glaxo SmithKline): group 1 at ages 6 and 12 months, group 2 at ages 12 and 18 months and group 3 at ages 15 and 21 months. We determined mothers' antibody to HAV (anti-HAV) status and infants' anti-HAV concentrations at the first vaccine dose (baseline) and at 1, 7 and 12 months thereafter. All were tested at age 13 months for responses to recommended routine vaccinations administered during infancy. Results: Of 248 participants, 140 were born to HA-susceptible mothers and 108 to immune mothers. At baseline, 34 of 36 (94%) group 1, 5 of 34 (15%) group 2 and one of 38 (3%) group 3 infants born to immune mothers were seropositive. By month 7, all participants in all groups were seropositive except group I infants born to immune mothers (34 of 36 [94%], seropositive). In group 1, peak geometric mean concentrations between infants born to immune (794 mIU/mL) and susceptible (2083 mIU/mL) mothers were significantly different. Across groups, peak geometric mean concentrations were similar among infants born to susceptible mothers (3166 mIU/mL, group 2; 3153 mIU/mL, group 3). Among infants born to immune mothers, the difference between groups 1 and 3 (2715 mIU/mL) was significant. There were no differences in responses to routine vaccinations. Conclusions: HA vaccine is immunogenic among infants born to HA-susceptible mothers and those born to immune mothers and vaccinated beginning >= 12 months old. Passively transferred maternal antibody persists for at least 6 months and results in a blunted response to HA vaccination.