Immunogenicity and Reactogenicity of Avaxim (160 AU) as Compared with Havrix (1440 EL.U) as a Booster Following Primary Immunization with Havrix (1440 EL.U) against Hepatitis A

Background: Hepatitis A vaccination is recommended for travelers from the UK to areas of moderate or high endemicity. Two licensed hepatitis A vaccines are now available in the UK, and this trial was undertaken to determine whether Avaxim can be used as a booster following a primary course of Havrix.
Methods: One hundred and eighty-five subjects were randomized to receive a booster dose of either Avaxim (n=92) or Havrix (n=93), 6 to 7 months after a primary dose of Havrix. Subjects were observed for 30 minutes for immediate reactions and subsequently completed a diary card for a further 2 weeks. Serology samples for HAV antibody titers were taken at 28 ± 7 days later.
Results: One month following the booster dose, all subjects in both treatment groups achieved HAV antibody titers ± 20 mlU/mL. In the Avaxim group, geometric mean liter (GMT) values increased from 642 mlU/mL (97.5% Cl 330–1250 mlU/mL) to 6669 mlU/mL (4566–9740 mlU/mL), compared with 739 mlU/mL (379–1443 mlU/mL) at baseline to 4460 mlU/mL (2880–6908 mlU/mL) following the administration of Havrix. The increase in GMT following the administration of Avaxim was significantly greater than that following Havrix (p=.02). Eight percent of subjects reported pain at the injection site following a booster dose of Havrix, compared with none following Avaxim. This difference in reactogenicity was statistically significant (p=.01). In all other respects, both preparations were safe and equally well tolerated.
Conclusion: Either Avaxim or Havrix may be given as a booster dose of hepatitis A vaccine when Havrix has been administered as the primary dose.