An analysis was carried out of the anti-haemagglutinin antibody responses in adult human recipients of inactivated whole virus A/Port Chalmers/1/73 (H3N2) vaccine using single radial diffusion combined with antibody adsorption techniques to determine antibody specificity. Antibody was characterised as cross-reactive (i.e. directed against antigenic determinants of haemagglutinin which are common for viruses within the H3 subtype) or strain-specific. Strain-specific antibodies for the vaccine strain and also for A/Hong Kong/68(H3N2) virus were assayed. A high proportion of vaccinees developed antibody of the cross-reactive specificity. The titre and frequency of such antibody increased with vaccine dose (100 iu to 1600 iu per dose). Many individuals developed strain-specific in addition to cross-reactive antibodies. A notable finding was that in 70% of vaccinees who developed strain-specific antibody, this was a paradoxical response directed against the strain specific determinant of A/Hong Kong/68 virus (the first number of the H3 subtype). Only 30% developed strain-specific antibody to the haemagglutinin of the vaccine strain. The percentage of vaccinees developing strain-specific antibodies to the vaccine strain was not significantly increased by increasing the dose of vaccine to 1600 iu. A second dose of A/Port Chalmers/73 vaccine administered approximately one year after the first dose only slightly increased the percentage with A/Port Chalmers strain-specific antibody.
Antibodies, Viral Cross Reactions