Clinical and laboratory observations following oral or intramuscular administration of a live attenuated hepatitis A vaccine candidate

Clinical observations made after immunising volunteers with a live attenuated hepatitis A vaccine are described. The candidate vaccine was prepared with the HM175 strain of hepatitis A virus and shown to be safe, immunogenic and efficacious in experimental animals. When the candidate vaccine was tested by oral administration in humans at increasing doses-10⁴, 10⁵, 10⁶ and 10⁷ median tissue culture infective doses (TCID₅₀)-an antibody response was not observed at any dose. Volunteers who received similar doses by the intramuscular route developed antibody to hepatitis A three weeks after immunization with 10⁶ or 10⁷ TCID₅₀. The antibody response was sustained for the 12 weeks of the observation period. All volunteers remained healthy with normal results from liver tests throughout the monitoring period. Further clinical observations of this product are in progress.