Background: Annual influenza immunization of healthcare workers (HCWs) is widely recommended to reduce the risk of healthcare-associated influenza (HAI). Although there is a clear association between higher HCW immunization and reduced incidence of HAI, data in acute care are lacking compared to the nursing home setting. Objective: Our goal was to assess the association between HCW influenza immunization and the incidence of HAI across 2 acute-care facilities. Methods: A multicenter prospective cohort study was undertaken at 2 acute-care hospitals including 1 university and 1 community-based academic hospital. Any patient prospectively identified with HAI was included between 2013–2014 and 2018–2019, whereas 2017–2018 was excluded due to vaccine mismatch. The HCW influenza immunization rate was defined as the proportion of HCWs (nurses and other allied and support staff but excluding physicians) immunized prior to December 15. A case of HAI was defined as laboratory-confirmed influenza A or B with symptom onset >72 hours after admission. The association between inpatient ward HCW influenza immunization rate and the incidence of HAI was compared using a Poisson regression analysis adjusting for hospital and influenza season. Results: Over 5 influenza seasons, the incidences of HAI at either facility were 0.24 and 0.22 per 1,000 patient days, whereas the median HCW influenza immunization rates were 57.3% (IQR, 42.5%–66.4%) and 66.6% (IQR, 50.6%–76.8%), respectively. When adjusting for hospital and influenza season in the multivariate analysis, HCW influenza immunization rates of 65% and 70% were not associated with HAI incidence. In contrast, HCW influenza immunization rates ≥75% was associated with a trend toward reduced HAI (IRR, 0.65; 95% CI, 0.39–1.08; P = .096) whereas inpatient wards above 80% immunization had significantly lower risk of HAI (IRR, 0.28; 95% CI, 0.089–0.89; P = .03). Conclusions: The risk of HAI across 2 acute-care hospitals was significantly lower among inpatient wards achieving HCW influenza immunization rates >80%. Acute-care facilities should aim for this minimum HCW immunization rate to protect patients from the complications of HAI.

Funding: None

Disclosures: None