Hemagglutination inhibition activity against homologous virus post-vaccination and post-challenge.

HI antibody titers were determined against A/Puerto Rico/8/1934 (H1N1) virus and are expressed as the reciprocal of the highest dilution of sera which inhibited hemagglutination of 4 HA units of virus. All values are expressed as geometric mean titers (GMT) of inhibiting sera from dilutions which offered a response. The numbers of positive sera are indicated as the number of positive sera/total number of sera. The range of titers and the GMT of the positive sera are listed in parentheses. HI titers less than 10 were below the limits of detection. Serum samples were not taken from mice which did not survive challenge (n. t.) or from mice which had not yet been vaccinated with either placebo or experimental formulations (–).#HI titers were significantly higher when compared to prime only doses.*Day 42 = challenge.