SUMMARYAntibody determinations against H3N2 and HINI type A influenza viruses were carried out on paired sera obtained from volunteers taking part in influenza virus vaccine studies, using both the haemagglutination-inhibition (HI) and single radial haemolysis (SRH) test. Good correlation between the HI and SRH test was found for both H3N2 and HI NI antibody and the zone area increases corresponding to significant SRH antibody rises determined for both virus strains. In both H3N2 and HiN1 vaccine studies, intranasal infection of the volunteers with live attenuated viruses was involved and by the measurement of HI and SRH antibodies prior to and following infection, levels of antibody equating with protection against the infecting viruses could be estimated. For the HI test the antibody titres associated with 500 protection were 42 for HI N 1, and 44 for H3N2 viruses; for the SRH test, 50 % protection was associated with zone areas of 200-25-0 mm2 for both HINI and H3N2 viruses.

Three synthetic vulpinic acids inhibited two influenza RNA viruses, type A (Philippine) and B (Paraha), in tissue culture with ID50 values ranging from 3.9 to 15.5 μg/ml. They had no activity against a third influenza virus or against two herpes viruses.