Countywide school-based influenza immunization: direct and indirect impact on student absenteeism.

OBJECTIVE: Live attenuated influenza vaccine was given to 5319 (44%) of the 12090 students enrolled in public elementary schools in Carroll County, Maryland, during the fall of 2005. We examined the impact of this community-based intervention on countywide student absenteeism during the subsequent influenza outbreak.
METHODS: This study used existing, anonymous information: census data, community influenza tests, and public school absenteeism data. The intervention group was Carroll County, years 2005-2006. The control group included Carroll County, years 2001-2005, and adjacent Frederick County, years 2001-2006. Weekly student absenteeism was determined during baseline influenza-free periods and influenza outbreak periods for all of the public schools.
RESULTS: The absolute change in absenteeism during the influenza outbreak periods over baseline in elementary schools was 0.61% for the intervention group and 1.79% for the control group. Similarly, the change in absenteeism during the influenza outbreak period over baseline for high schools was 0.32% for the intervention group and 1.80% for the control group. Although not statistically significant, trends in middle schools were similar.
CONCLUSIONS: Countywide school-based influenza vaccination was associated with reduced absenteeism during an influenza outbreak. The data suggest not only a direct impact on elementary schools but also an indirect impact on high schools. School-based programs provide an efficient method of providing influenza vaccination to children, and protection may extend to unvaccinated community members. Additional research is needed to determine whether school-based vaccination of children reduces morbidity and mortality associated with influenza outbreaks.