Immune response to influenza vaccination of elderly people. A randomized double-blind placebo-controlled trial.

The objective of this study was to determine the immune response to influenza vaccination in elderly people, using a randomized, double-blind, placebo-controlled trial. Venous blood was taken from 1838 people aged 60 years and older, prior to injection with the influenza vaccine or a placebo. A second blood sample was taken three weeks later. The antibody reaction was measured by comparing the geometric mean titre and the percentage of participants who had a protective antibody titre before and after vaccination and for all sera of each strain. A protective antibody titre was found in 43-68% of those who had received the vaccine, depending on the strain investigated. Patients potentially at risk showed a response similar to the other participants. We conclude that influenza vaccination in elderly people provides a reasonable to good immune response. Research is needed on whether a good immune response decreases the incidence of influenza.