Vaccination against hepatitis A: comparison of different short-term immunization schedules.

A total of 114 healthy young adults were immunized with hepatitis A vaccine using different vaccination schedules. Individuals received either a single dose (group 1), two doses given simultaneously (group 2), two doses at days 0 and 14 (group 3) or at days 0 and 28 (group 4), or three doses at days 0, 7 and 21 (group 5). Two weeks after a single dose, seroconversion rates between 77 and 85% were achieved (groups 1, 3, 4). All individuals immunized with two doses within two weeks (groups 2, 3, 5) had antibodies to hepatitis A vaccine (anti-HAV positive) by week 3; these participants also showed clearly higher mean anti-HAV values (geometric mean titres, GMTs) at this time than those individuals vaccinated only once. GMTs at week 8 were 560 IU/l in group 5, 236, 339 and 428 IU/l in groups 2-4 and 102 IU/l in group 1. Of participants with anti-HAV at week 8, 82 were again tested 4 months later; all were still seropositive. Ten individuals were tested during the first three weeks at 3-4 day intervals for anti-HAV immunoglobulin M (IgM); specific IgM responses were not detectable before day 10 but were present in eight of 10 vaccinees by day 14.