Countywide School-Based Influenza Immunization: Direct and Indirect Impact on Student Absenteeism

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Abstract
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.