Long-term persistence of antibodies induced by vaccination and safety follow-up, with the first combined vaccine against hepatitis A and B in children and adults.

It is important to monitor the long-term persistence of antibodies induced by vaccination. Four cohorts were followed for their long-term immunity after vaccination with a combined hepatitis A and B vaccine (Twinrix; SmithKline Beecham Biologicals, Rixsenart, Belgium). Two cohorts of adults (ages 17-60 years), one of 1-6-year-olds, and one of 6-15-year-olds were vaccinated following a 0, 1, and 6-month schedule. Follow-up data until month 72 (adults) and month 60 (children) are available. At month 72, antibody to hepatitis A virus (anti-HAV) seropositivity (S+) was 100% for both adult cohorts (n = 40 and n = 47) and 95% and 89% of the vaccinees were seroprotected against hepatitis B virus (HBV), respectively. The geometric mean titres (GMTs; mIU/ml) for anti-HAV were 977 and 542 and the GMTs for the antibody to hepatitis B surface antigen (anti-HBs) were 322 and 90. For 1-6-year-olds at month 60 (n = 39), anti-HAV S+ was 100% with a GMT of 479 and 97% were protected against HBV with a GMT of 195. At month 60 for the 6-15-year-olds (n = 42), anti-HAV S+ was 100% with a GMT of 990 and 95% were protected against HBV with a GMT of 263. There have been no safety issues during the follow-up. In the past 5 years, a postmarketing surveillance system was available. Using this system, all spontaneous adverse events are collected and archived. Although infrequent, the most commonly reported adverse events after more than 13 million doses were allergic-type reactions followed by fever and injection site reactions. The combined hepatitis A and B vaccine is safe and is well tolerated. Immunity provided by the vaccine remains high in adults and children with comparable results to those obtained with monovalent vaccines.