The impact of influenza vaccination on respiratory illness at a boarding school.

We studied the impact of influenza vaccine during an outbreak of influenza at a 989-student boarding school in January to March, 1989. By February 6, 120 (17%) of 690 students completing survey questionnaires had been ill with fever and respiratory symptoms. Eighty-seven students had received influenza vaccine in the previous 18 months; these students had an attack rate half that of the unvaccinated students (9% v 19%; vaccine efficacy = 50%, confidence interval = 0%-70%). We estimate that, if the entire student body had been vaccinated, influenza-like illness could have been prevented in 162 students (16% of the school), and that preventing this illness could have avoided at least 482 student-days of missed classes, or approximately one student-day for each 1.8 additional doses of vaccine given. This study suggests that, when feasible, a broad influenza immunization policy for healthy students at residential schools should substantially decrease the disruption of school activities caused by influenza.