[Active immunization against hepatitis A. Comparison of various immunization schedules]. 
Three different immunization schedules were compared in 144 young, healthy adults (81 men, 63 women; mean age 28.5 years).  They were randomly assigned to one of three groups: group 1, immunization shots on day 0 and day 14 (n = 47), group 2, on day 0 and day 28 (n = 50), and group 3, on day 0, 14 and 28 (n = 47).  All participants had a booster shot after one year.  The seroconversion rate was 40-46% after first shot, 95-100% after the second one; all were anti-HAV positive after the booster injection.  All subjects had specific antibodies in a mean concentration of > 400 IU/l two weeks after the second shot.  In almost all subjects antibodies were demonstrable up to the 12th month after the first immunization (> 20 IU/l).  Mean antibody concentration during the interval between the second and third immunization after basal immunization on day 0 and 14 or 0 and 28, respectively, was comparable.  Three initial immunizations 14 days apart did not achieve much higher anti-HAV levels.  The vaccine was equally well tolerated in all three groups.  Thus basal immunization shortened to two injections two weeks apart presents a good alternative to the standard scheme of two injections four weeks apart.  Three injections two weeks apart bring no demonstrable advantage.