Field trial of live attenuated influenza A/B ("Alice"/R-75) vaccine

The reactogenicity, immunogenicity and protection effecacy of a serum inhibitor-resistant live attenuated influenza A/B ("Alice"/R-75) vaccine was determined in a group of health young volunteers. The influenza A component was derived from A/England/42/72 (H3N2) strain, and the B component from B/Hong Kong/5/72 strain. Sixty-eight subjects had hemagglutination inhibition (HAI) antibody titers to influenza A hemagglutinin (HA) antigen of less than or equal to 1:8 ("low A" group) and 75 had similarly low antibody titers to B HA antigen ("low B" group). Two inocula given 14 days apart consisted of vaccine in two doses (VV); one dose of vaccine followed by placebo (VP); or two doses of placebo (PP). The reactogenicity of the vaccine was low, with approximately 25% of subjects in both the immunized and placebo categories having symptoms mainly of respiratory nature. The A component of the vaccine was immunogenic with 90.9% of the subjects in the low A group VV category showing seroconversion. By contrast, only 20% of VV subjects in the low B group seroconverted to B antigen. The vaccine afforded significant protection againndergone a slight antigenic drift. There was no difference in protection afforded either by one or two doses of the vaccine. Thus the overall protection efficacy following at least one dose of the vaccine was 80.0% (p = .01), and in the low A group subjects it was 85.5% (p = .01).