Efficacy of minimal doses of an American hepatitis B vaccine in neonates.

Eight neonates and three young children at risk for hepatitis B infection were vaccinated with minimal doses of inactivated hepatitis B vaccine. The purpose of the study was to evaluate the efficacy of low doses with a view toward reducing the cost of immunization and therefore extending the practice to a larger number of subjects and minimizing the incidence of adverse reactions to the vaccine. The patients received two intramuscular injections (0.1 ml) of vaccine at a two-month interval and a booster six months after the first dose. Anti-HBs titers were determined simultaneously by radioimmunoassay on all serum samples collected. Five of the 11 patients achieved presumably protective (greater than 10 mU/ml) antibody levels within six months after the first dose (titers between 10 and 74 mU/ml), and all but one patient achieved titers between 27 and 2,500 mU/ml within two months after the booster. No adverse reaction was observed.

RIA evaluation of antibody levels in neonates from HBsAg-positive mothers after active, passive, and combined immunoprophylaxis.

We evaluated the anti-HBs titers in 20 babies born to HBsAg-positive mothers and receiving different programs designed to prevent hepatitis B. Passive prophylaxis by HBIG for 6 months assured detectable antibody levels in the same period. 3 months after the last injection we could detect antibodies in 5 out of 9 cases. In no case could we detect antibodies 6 months after the last dose. Active prophylaxis by hepatitis B vaccine was able to raise anti-HBs response in 8 out of 12 babies after two or three very small doses (1.25 micrograms of antigen). 2 of these babies were given the first dose at birth. Small doses of vaccine were immunogenic in the presence of passive antibodies.