City-wide school-located influenza vaccination: a retrospective cohort study

Background We measured the effectiveness of a city-wide school-located influenza vaccination (SLIV) program implemented in over 102 elementary schools in Oakland, California. Methods We conducted a retrospective cohort study among Kaiser Permanente Northern California (KPNC) members of all ages residing in either the intervention or a multivariate-matched comparison site from September 2011 - August 2017. Outcomes included medically attended acute respiratory illness (MAARI), influenza hospitalization, and Oseltamivir prescriptions. We estimated difference-in-differences (DIDs) in 2014-15, 2015-16, and 2016-17 using generalized linear models and adjusted for race, ethnicity, age, sex, health plan, and language. Results Pre-intervention member characteristics were similar between sites. Among school-aged children, SLIV was associated with lower Oseltamivir prescriptions per 1,000 (DIDs: −3.5 (95% CI −5.5, −1.5) in 2015-16; −4.0 (95% CI −6.5, −1.6) in 2016-17) but not with other outcomes. SLIV was associated with lower MAARI per 1,000 in adults 65+ years (2014-15: −13.2, 95% CI −23.2, −3.2; 2015-16: −21.5, 95% CI −31.1, −11.9; 2016-17: −13.0, 95% CI −23.2, −2.9). There were few significant associations with other outcomes among adults. Conclusions A city-wide SLIV intervention was associated with lower Oseltamivir prescriptions in school-aged children and lower MAARI among people over 65 years, suggesting possible indirect effects of SLIV among older adults.