Failure of influenza vaccine to prevent two successive outbreaks of influenza A H1N1 in a school community.

Forty nine of the 149 boys (33%) at a preparatory school fell ill at the beginning of the autumn term 1986 with symptoms of influenza. One hundred and eighty two of the 470 pupils (39%) in the senior part of the same school had similar symptoms of influenza at the beginning of the spring term 1987. A new variant of influenza A H1N1 virus was isolated from both outbreaks and shown to be antigenically similar to A/Taiwan/1/86. The attack rate among pupils who had previously received trivalent influenza vaccine containing A/Chile/1/83 H1N1 antigen was not significantly different from the rate among those who had never been vaccinated. It is concluded that annual vaccination of all boarding school pupils may be inappropriate.