Antibody Response and Immune Memory 15-18 Years After HBV Vaccination

Taiwan is an endemic region for hepatitis B. Before the implementation of a nationwide vaccination program in 1984, the hepatitis B virus (HBV) carrier rate in the general population was 15 to 20%.1-2 The major impact of hepatitis B (HB) infection is its long-term sequelae which may include chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma.3 Perinatal infection accounts for 40-50% of all hepatitis B infections and is responsible for the generation-to-generation transmission of HB virus.4 Hepatitis B vaccines, both plasma derived and recombinant, are highly immunogenic and efficacious.5-10 It has been reported that HB vaccine given soon after birth is able to protect infants from perinatal infection and HB infection became the first disease model to show that mother-to-neonate transmission can be interrupted by an effective vaccine.11 Taiwan started a national program of HB vaccination since 1984. This program resulted in a significant reduction of the HB carrier rate in children aged below 10 years from 9.8% before nationwide vaccination to 1.3% after the program.12 It also decreased the incidence of hepatocellular carcinoma in children aged 6 to 9 years from 0.52 to 0.13 per 100,000.13 However, the duration of protection provided by the HB vaccine and the proper timing of a booster dose remains unclear. Because the HB vaccine is a subunit protein vaccine, which contains only HBsAg, a limited duration of protection is anticipated. The results of several long-term follow-up studies of the protective efficacy of HB vaccination have been published. Soon after vaccination, protective levels of antibody (anti-HBs \>10 mIU/mL) can be detected in the great majority (83-99%) of vaccinees.5-7 The proportion of vaccinees with protective anti-HBs levels decreases to 75-87% 5 years after vaccination and further drops to 50 to 70% 10-12 years after.10,11,14,15,19-21 Because of the progressive decline of anti-HBs and the associated increased likelihood of developme