Immunization of elderly volunteers with the 1988-89 inactivated whole influenza vaccine: assessment of antibody responses by haemagglutination inhibition and single radial haemolysis tests.

The immunogenicity of inactivated whole trivalent influenza vaccines (A/Taiwan/1/86 (H1N1), A/Sichuan/2/87 (H3N2), and B ijing/1/87) recommended for the 1988-89 winter season was evaluated in 236 elderly (mean age 71 years) high risk volunteers. An overall significant increase in the number of subjects with protective haemagglutination inhibiting (HI) antibodies (titer > 1:40) against vaccine components was observed after vaccination. Nevertheless, a percentage of individuals (ranging from 56% to 62%) remained without protective antibodies and the number of people showing a positive response was limited (from 32% to 41%). By the comparative analysis of the results obtained examining the presence of protective levels of antibody in the sera from 91 volunteers using HI versus the single radial haemolysis (SRH) test, we obtained evidence for a higher sensitivity of SRH technique especially against B antigen.