Efficacy of a heat inactivated hepatitis B vaccine in male homosexuals: outcome of a placebo controlled double blind trial.

The efficacy of a heat inactivated hepatitis B virus vaccine, containing 3 micrograms hepatitis B surface antigen (HBsAg), was studied in a high risk group of 800 susceptible homosexual men by a randomised placebo controlled double blind trial. At the trial end point (21.5 months), 17 hepatitis B virus infections had occurred in vaccinated subjects (attack rate 4.8%) and 56 in subjects receiving a placebo (attack rate 23.8%). This reduction in the incidence of hepatitis B virus infections in vaccinated subjects was highly significant (p less than 0.0001). Two months after the first injection 72.3% of the vaccinated subjects had formed antibodies against hepatitis B surface antigen, and this percentage increased to 89% at four months. Maximum anti-HBs titres were reached five months after the first vaccination, the geometric mean titre being 107.6 mIU. Even vaccinated subjects with a low antibody response (greater than or equal to 1 and less than 10 mIU) were found to be protected from HBsAg-positive infections. The vaccine had no serious side effects.