Comparison of the reactogenicity and immunogenicity of a split and a subunit-adjuvanted influenza vaccine in elderly subjects.

A randomised, open study was carried out among an elderly population in order to compare the reactogenicity and immunogenicity of an inactivated, split virion influenza vaccine (Vaxigrip, Aventis Pasteur MSD, Lyon, France) with that of an MF59-adjuvanted, subunit vaccine (Fluad, Chiron Vaccines, Siena, Italy). Both vaccines contained the three strains: A/Sydney/5/97 (H3N2), A/Beijing/262/95 (H1N1) and B/Beijing/184/93, recommended by the WHO for the 1998-1999 influenza season. A total of 2150 subjects were vaccinated and included in the reactogenicity analysis. A total of 1076 subjects received Vaxigrip (age 73.3 +/- 5.9 years, 49.6% men) and 1074 subjects received Fluad (age 73.4 +/- 5.9 years, 52.3% men). All subjects were kept under medical observation for 30 min after vaccination, in order to check any immediate local and/or systemic reaction. A self monitoring diary card was given to all subjects to collect any local and/or systemic reaction occurring during the 3 days following the vaccination, any adverse event occurring between vaccination day and 21st day post-vaccination and any medication taken during the study period. A total of 1186 subjects were included in the immunogenicity analysis. A total of 591 subjects received Vaxigrip (age 73.4 +/- 5.6 years, 52.3% men) and 595 subjects received Fluad (age 73.8 +/- 5.9 years, 55.8% men). Blood samples were collected pre- and 21 days post-vaccination and were analysed by the haemagglutination inhibition assay. In terms of reactogenicity both vaccines were generally well tolerated. The frequency of local reactions was lower in the group that received Vaxigrip. Pain at the injection site occurring from 30 min to 3 days after vaccination was also significantly less frequent (P = 0.005) in the Vaxigrip group. Fever > or =37.5 degrees C was reported in less than 1% of all vaccinated subjects. No serious adverse event was related to vaccine administration. In terms of immunogenicity both vaccines induced an effective immune response (anti-HI titre > or =40) against A/Sydney/5/97 (H3N2) and A/Beijing/262/95 (H1N1) strains in the entire population. Vaxigrip and Fluad induced similar seroprotection and seroconversion rates against the A/Sydney/5/97 (H3N2) strain. For both vaccines a lower percentage of subjects achieved a seroprotective titre > or =40 against the B/Beijing/184/93. A lower antibody response against the influenza B strain was also observed in other studies conducted during the same season. In subjects 75 years of age or older, Fluad was more immunogenic than Vaxigrip for all three virus strains.