Influenza vaccines: antibody responses to split virus and MF59-adjuvanted subunit virus in an adult population.

The humoral immune response generated by two commercial influenza vaccines was evaluated in a randomised, double-blind trial performed in the Public Department of Dolo Health District (North-east Italy) during the winter season 1997-1998. Ninety-eight subjects were immunised with a split virus vaccine and ninety-six with a MF59-adjuvanted subunit virus vaccine (SU/MF59). The pre- and postvaccination (approximately 30 days) antibody titres were determined by hemagglutination inhibition test (HI). After immunisation protective titre rates (> or = 1:40) were near 100% against virus A strain and 82.5% against B strain. Both vaccines caused significant rises in geometric mean antibody titres (GMTs); however, people who received SU/MF59 vaccine were found to develop a greater immune response compared to the group immunised with SVV. According to logistic regression analysis the unprotective prevaccination immune status and the use of SU/MF59 were identified as independent factors significantly increasing the response to immunisation.