Long-term immunogenicity andefficacy ofa reduced doseofplasma-based hepatitis B vaccine inyoungadults

A cohort ofseronegative preclinical medical anddental students andanother cohort ofseronegative national service recruits whowereimmunized intramuscularly withareduced dose(10pg)ofplasmabasedhepatitis B vaccine (Merck, Sharp& Dohme)atthestart ofthestudyandat1monthand6 monthsthereafter werefollowed upfor5yearsand6years, respectively. Amongthemedical anddental students, antibody tohepatitis B surface antigen (anti-HBs) (>10mIUlml) wasdetected in81%ofthe vaccinees attheendofthe5-year follow-up andthegeometric meantitre (GMT)haddropped from 412.6mIU/ml oneyearafter completion ofvaccination to174.9 mIUlml after 5years. Antibody tohepatitis B coreantigen (anti-HBc) wasdetected in0.4-1.0% ofthevaccinees butnonewaspositive for hepatitis Bsurface antigen (HBsAg) during thefollow-up period. Amongthenational servicemen, theanti-HBs seroconversion rateandGMT wereconsiderably lower thanthose ofthepreclinical medical anddental students. Attheendofthe6-year follow-up, 55% ofthevaccinees werepositive foranti-HBs (>10mlU/ml) andtheGMThaddropped from80.7mIUlml oneyearafter completion ofvaccination to30.4mlU/mlafter 6 years. Anti-HBc wasdetected in8 (2.7%) andtransient HBsantigenaemia in2 (0.7%) of293vaccinees after 4years. However, noneof the196vaccinees followed upat6yearswasHBsAg-positive compared with8 (4.2%) of191seronegative national service recruits whowerenotvaccinated, giving a vaccine efficacy of100%inthe prevention ofthechronic HBsAgcarrier state.