Efficacy of hepatitis B vaccine in chimpanzees given transfusions of highly infective blood

The protective efficacy of a hepatitis B vaccine against infections from transfusions of large volumes of highly infective blood in five immunized chimpanzees was assessed. Hepatitis B surface antigen (HBsAg) became positive and antibody to HBsAg (anti-HBs) disappeared soon after transfusion in the five chimpanzees. Two chimpanzees that had HBsAg only on the day of transfusion did not develop infection. However, the remaining three chimpanzees with persistent HBsAg antigenemia for three to four days developed serologic evidence of infection. Two chimpanzees did not have hepatitis and the third had a mild, transient case of acute hepatitis. The hepatitis B vaccine prevented the four immunized chimpanzees from developing illness. The remaining chimpanzee developed hepatitis, but a rapid booster response of anti-HBs owing to the previous vaccination appeared to lighten the severity of the disease and prevent chronicity.