Correlation between rate of infection and preexisting titer of serum antibody as determined by single radial hemolysis during and epidemic of influenza A/Victoria/3/75.

During an outbreak of infection with wild-type influenza A/Victoria/3/75 virus, a correlation was established between the rate of infection and the preepidemic titer of serum antibody to that virus as measured by the single radial hemolysis technique. Titers of antibody determined by the hemagglutination inhibition method as well as by the single radial hemolysis technique were directly correlated with the rate of infection. By use of the single radial hemolysis technique, the 50% protective titer of antibody was calculated for a population of recipients of live influenza A/Victoria/3/75 virus vaccine.