Hepatitis A vaccine: persistence of antibodies 5 years after the first vaccination.

The recent development of safe and effective inactivated hepatitis A vaccines provides the opportunity to control hepatitis A. However, effective control will depend upon the duration of protection provided by the vaccine. Evaluation of persistence of antibodies over time is essential for the determination of vaccination schedules and strategies. For this purpose blood samples were obtained from 140 volunteers, 5 years after the administration of three 720 ELISA units (EU) doses of an inactivated hepatitis A vaccine according to a 0, 1 and 6 month schedule. All serum samples were tested for anti-hepatitis A virus (HAV) antibodies using a sensitive ELISA inhibition assay. All subjects, except one, had anti-HAV titres > or = 20 mIU ml-1. The geometric mean titre (GMT) was 1258 mIU ml-1. All individual titres were at least 10 times higher than the minimum protective level. According to the rate of antibody level decrease over time, the predicted duration of antibodies is estimated to be at least 20 years.