HEPATITIS-A VACCINE - A NEW CONVENIENT SINGLE-DOSE SCHEDULE WITH BOOSTER WHEN LONG-TERM IMMUNIZATION IS WARRANTED

A total of 162 anti-HA V-negative healthy adults were immunized with a single high dose (1440 ELISA units = 1 ml) of inactivated hepatitis A vaccine and a booster was given at month 6. Antibodies were measured after modification ofa commercial ELISA kit, enabling quantification o f titres down to 6 mIU ml(-1). After 14 days, 96% of vaccinees had pos itive anti-HAV titres (>20 mIU ml(-1)), and after 30 days all vaccinee s had seroconverted. The geometric mean titres were 150 mIU ml(-1) and 380 mIU ml(-1) respectively. The booster dose at month 6 elicited a d ramatic (25-fold) increase in antibody titres from 125 to 3090 mIU ml( -1). Thus a single dose may be a convenient alternative to immunoglobu lin for inducing rapid seroprotection, with a booster dose at month 6 ensuring long-lasting protection.