Successful Booster Antibody Response up to 54 Months after Single Primary Vaccination with Virosome-Formulated, Aluminum-Free Hepatitis A Vaccine

This study demonstrates that a booster dose of the virosome-formulated, aluminum-free hepatitis A vaccine Epaxal (Berna Biotech) is highly immunogenic in subjects who received a single primary dose of this vaccine 18–54 months earlier. There were no significant differences in geometric mean antibody titers (GMTs) among subjects who received the booster dose 18–29 months (GMT, 2330 mIU/mL), 30–41 months (GMT, 2395 mIU/mL), or 42–54 months (GMT, 2432 mIU/mL) after primary vaccination, indicating that delays in the administration of booster vaccination do not lead to a loss of immunogenicity.