HAV vaccine works despite maternal antibodies

Infants and children aged younger than 2 years who are vaccinated against hepatitis A virus (HAV) show persistent seroprotection whether they received antibodies to the virus from their mothers, a new study reports. Protection persists for at least 10 years in most children, regardless of maternal antibody status.

The study randomized 197 infants and children aged younger than 2 years to receive 2 doses of inactivated hepatitis A vaccine at 6 and 12 months, 12 and 18 months, or 15 and 21 months. Within each of the 3 groups, children were randomized by presence or absence of maternal antibodies to HAV (maternal anti-HAV). Passive transfer of maternal anti-HAV to the infant may decrease immune response to the hepatitis A vaccine.

Researchers measured anti-HAV levels in serum samples at 1 and 6 months after the second vaccine dose, then at 3, 5, 7, and 10 years. At 1 month, all children showed evidence of seroprotection (defined as >10 mIU/mL). More than 95% of children vaccinated at 12 and 18 months and at 15 and 21 months retained seroprotection continuously through 10 years of age. Although children vaccinated at 6 and 12 months had the lowest antibody response to vaccination after the first dose, less than 12% lost seroprotection 7 to 10 years after the second dose.

The study found higher concentrations of anti-HAV antibody in children vaccinated after 12 months, which supports current guidelines recommending routine vaccination of US children against HAV beginning at 12 months.

The finding of high persistence of seroprotection among children immunized starting at 6 months might warrant further research into use of the vaccine in children aged younger than 12 months, for example, in countries with significant HAV infection early in life or for preexposure or postexposure prophylaxis in children aged 6 to 12 months when immunoglobulin is not available.

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