Influenza immunization: serologic and clinical responses in military units

Two inactivated influenza-virus vaccines were tested and compared in three army training units in Israel. The serological responses to the vaccines and the side-effects were assessed. The vaccines contained the influenza strains which were prevalent in 1974: A2/Port Chalmers/1/73 and B/Hong Kong/8/73. One of the vaccines also contained A2/England/42/72. Both vaccines caused a more than three-fold rise in geometric mean titers against influenza A strains, and about a twofold rise in geometric mean titers against influenza B/Hong Kong/5/73. Approximately 75%-80% of the vaccinees acquired protective hemagglutination-inhibition antibody titers against influenza A strains, while less than 30% acquired protective titers against B strains. In general, there were no significant differences between the serological responses to the two vaccines. More than 50% of the vaccinees experienced at least one systemic side-effect (50.3% with one vaccine and 61.0% with the other). The average number of side-effects per person was between 1.78 and 2.11. However, these side-effects were generally of short duration and caused minimal disability. On the whole, the two vaccines did not differ significantly with regard to the side-effects they caused.