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. The proportion of KPNC members vaccinated for influenza by KPNC or the SLIV program was 8–11% higher in the intervention site than the comparison site during the intervention period. 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 higher influenza vaccination coverage, lower Oseltamivir prescriptions in school-aged children, and lower MAARI among people over 65 years, suggesting possible indirect effects of SLIV among older adults.