Immunogenicity Study of an Inactivated Hepatitis A Vaccine in Infants and Young Children
Immunogenicity Study of an Inactivated Hepatitis A Vaccine in Infants and Young Children
Infants born to immune mothers and therefore having passively-transferred maternal antibody
 (PMA) to hepatitis A virus (HAV) have a blunted immune response to hepatitis A vaccine. We
 compared the immunogenicity of hepatitis A vaccine among infants with and without PMA,
 vaccinated on different schedules. We found that when vaccination is begun at or after 12
 months of age, there was no difference in the immune response to the vaccine between infants
 born to immune vs. susceptible mothers.
Background: Infants with passively-transferred maternal antibody (PMA) to hepatitis A virus
 (HAV) have a blunted immune response to hepatitis A vaccine. We compared the immunogenicity
 of hepatitis A vaccine among infants with and without PMA, vaccinated on different schedules.

 Methods: Infants were randomized to one of three groups, each receiving two doses of 720
 EL.U. of hepatitis A vaccine (HAVRIX, Glaxo SmithKline) according to the following schedules:
 Group 1 at ages 6 and 12 months; Group 2 at ages 12 and 18 months; Group 3 at ages 15 and 21
 months. We determined antibody to HAV (anti-HAV) status of mothers at the time of delivery,
 and measured infants' anti-HAV concentrations at the time of the first vaccine dose
 (baseline), and at 1, 7 and 12 months thereafter. Anti-HAV concentrations > 33
 milli-International Units/milliliter (mIU/mL) were considered protective. We monitored
 adverse reactions using diary cards and chart reviews.

 Results: A total of 239 infants were enrolled, including 134 born to anti-HAV negative
 mothers (Groups 1N, 2N, 3N) and 105 born to anti-HAV positive mothers (Groups 1P, 2P, 3P).

 At month 12, 6 months after the second vaccine dose, the difference in GMC between Groups 1P
 and 1N was the only statistically significant difference within groups (p<0.05). There were
 no statistically significant differences in GMC among groups of infants born to anti-HAV
 negative mothers ("N" groups), but the difference between Group 1P and Group 3P infants was
 significant (p < 0.05). No serious adverse reactions related to vaccination were detected.

 Conclusions: Hepatitis A vaccine is immunogenic among infants born to anti-HAV negative
 mothers, and among those born to anti-HAV positive mothers and vaccinated beginning as young
 as 12 months old. The persistence of PMA for at least six months among the majority of
 infants born to anti-HAV positive mothers results in lower seroconversion rates and GMC's.
Inclusion Criteria:term infant with normal growth and development, considered to be healthy
 at age 6 months; written informed consent by parent/guardian -

 Exclusion Criteria:received or expected to receive immune globulin or blood/blood products
 while enrolled; received or expected to receive immunosuppressive therapy within 30 days of
 vaccination or has immune deficiency; currently enrolled in another vaccine trial;
 progressive or unstable neurological disorder

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