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Adjuvanted Influenza Vaccine and Influenza Outbreaks in US Nursing Homes: Results From a Pragmatic Cluster-Randomized Clinical Trial.

Gravenstein S, McConeghy KW, Saade E, Davidson HE, Canaday DH, Han L, Rudolph J, Joyce N, Dahabreh IJ, Mor V. Adjuvanted Influenza Vaccine and Influenza Outbreaks in US Nursing Homes: Results From a Pragmatic Cluster-Randomized Clinical Trial. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 2021 Dec 6; 73(11):e4229-e4236.

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BACKGROUND: Influenza outbreaks in nursing homes pose a threat to frail residents and occur even in vaccinated populations. We conducted a pragmatic cluster-randomized trial comparing adjuvanted trivalent influenza vaccine (aTIV) versus trivalent influenza vaccine (TIV). We report an exploratory analysis to compare the effect of aTIV versus TIV on facility-reported influenza outbreaks. METHODS: We evaluated the impact of the intent-to-treat vaccine assignment on outbreaks reported from November 2016 to March 2017. We collected data according to standard CDC definitions for both suspected outbreaks and those with a laboratory-confirmed case and adjusted for facility-level vaccination rates and resident characteristics in nursing homes. RESULTS: Of 823 randomized nursing homes, 777 (aTIV, n = 387; TIV, n = 390) reported information on influenza outbreaks. Treatment groups had similar characteristics at baseline except for race/ethnicity: homes assigned to TIV had a higher percentage of African-American residents (18.0% vs 13.7%). There were 133 versus 162 facility-reported suspected influenza outbreaks in aTIV versus TIV facilities, respectively; of these, 115 versus 140 were laboratory confirmed. The aTIV group experienced a 17% reduction in suspected (rate ratio, .83; 95% confidence interval, .65-1.05) and laboratory-confirmed (.83; .63-1.06) influenza outbreaks. Covariate adjustment increased the estimated reduction for suspected outbreaks to 21% (.79; .61-.99) and 22% for laboratory-confirmed outbreaks (.78; .60-1.02). CONCLUSIONS: In an exploratory analysis of a cluster-randomized trial we observed 17-21% fewer outbreaks with aTIV than TIV. Clinical Trials Registration. (NCT02882100).

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