Background: School-located influenza vaccination programs aim to increase influenza vaccination coverage and produce indirect effects by interrupting influenza transmission. We evaluated the impact of a program that delivered the inactivated influenza vaccine in 2016-17 to elementary schools in a large, diverse urban school district in Oakland, California on vaccination coverage, school absenteeism, and influenza hospitalization.
Methods: We conducted a prospective cohort study and used pre-program data from the California Department of Education on school characteristics to identify a control school district with similar characteristics to the program district. We measured parent recall of student influenza vaccination in surveys in 2017 in 44 schools per district (N=6,070). We obtained absence data from school districts and influenza hospitalization data for district catchment areas prior to and during the program. We used generalized linear models to estimate difference-in-differences (DIDs) in absence rates during influenza season adjusting for month, race, and grade to account for differences in pre-program rates. Standard errors accounted for school clusters. For influenza hospitalization, we estimated cumulative incidence rates using census data to obtain the population size and risk ratios (RR) using modified Poisson regression.
Results: Vaccination coverage was 56.7% in control schools and 63.9% in program schools (difference = 7.2%; 95% CI 3.6%, 10.8%). 24% of students in program schools were vaccinated at school. Absences per 100 days were 5.40 vs. 6.68 in program vs. control sites for all absences and 3.01 vs. 3.60 for illness-related absences; DIDs were statistically significant for illness absences. Among all ages, the risk ratio for influenza hospitalization in program vs. control districts was 0.65 (95% CI 0.55, 0.78) among all ages and 0.71 for adults 65 or older (95% CI 0.57, 0.89). Hospitalization was too rare among elementary aged students to estimate RRs in that group.
Conclusion: Elementary school-located influenza vaccination increased influenza vaccination and decreased school absence and influenza hospitalization. There was an indirect effect on hospitalization in the elderly and non-elementary aged groups.
J. Benjamin-Chung, None
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