Evidence of effectiveness from a large county-wide school-based influenza immunization campaign

A school-based campaign in Knox County, TN immunized 41% and 48% of school children with live attenuated influenza vaccine in 2005 and 2006, respectively. We computed the relative risk (RR) of a positive rapid influenza test in Knox compared to Knox-surrounding county children (controls) during five baseline and two campaign seasons. Among children aged <5 years, the RR for a positive test remained relatively constant throughout the study seasons. Among children aged 5-17 years (target population), the RR was 1 during baseline and declined by 21% (RR, 0.79; 95% CI, 0.59-1.05) and 27% (RR, 0.73; 95% CI, 0.60-0.87) during the first and second campaign season, respectively. These findings suggest a direct beneficial effect of the immunization campaign.