Immunogenicity of an inactivated hepatitis A vaccine in Dutch United Nations troops

Limited information existed on the immunogenicity of an inactivated hepatitis A vaccine as part of an extensive vaccination schedule. Dutch marines bound for duty in Cambodia received inactivated hepatitis A vaccine (720 ELISA units of antigen, two intra-gluteal doses at a 2-week interval before departure and an intra-deltoid booster vaccination after 8 months) simultaneously with several other vaccines. Hepatitis A antibodies were determined in blood-samples drawn before and after the booster vaccination, using two laboratory tests (modified HAVAB and SBB-ELISA). At 8 months, before the booster vaccination, 52% (modified HAVAB) and 81% (SBB-ELISA) had seroconverted. Risk factors for non-seroconversion were increasing age and a typhoid vaccination. At 11 months 97.6% (modified HAVAB) and 100% (SBB-ELISA) had seroconverted. Non-seroconversion at 8 months was remarkably high. SBB-ELISA was more sensitive in lower titre ranges.