ArticleOpen forum infectious diseases2026
Recombinant Influenza Vaccine and Influenza Outbreaks in US Nursing Homes: Results From a Pragmatic Cluster-Randomized Clinical Trial.
Article in Open forum infectious diseases, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
Background: Influenza outbreaks in US nursing homes contribute substantially to morbidity, mortality, and operational strain. Recombinant influenza vaccine may reduce transmission in long-term care settings, but high-quality evidence to support this effect is limited. The purpose of this study was to compare the risk of influenza outbreaks (influenza confirmed: 1 or more laboratory-confirmed cases; influenza suspected: 2 or more influenza-like illness cases) among nursing homes randomized to recombinant quadrivalent influenza vaccine (RIV4) vs standard-dose egg-based inactivated quadrivalent influenza vaccine (IIV4). Methods: This study was a pragmatic, cluster-randomized clinical trial conducted across 2 influenza seasons (n = 965 facilities in 2019-2020 and n = 1023 in 2020-2021) in Medicare-certified US nursing homes. Nursing homes with ≥50 long-stay residents and high proportions of adults aged ≥65 years were eligible and assigned to RIV4 or IIV4 for resident and staff vaccination. The outcome was facility-reported influenza outbreaks, assessed by monthly logs. Results: During the 2019-2020 season, RIV4-assigned facilities experienced fewer suspected (148 [30.6%] vs 178 [37.0%]) and laboratory-confirmed (177 [36.6%] vs 214 [44.5%]) influenza outbreaks than IIV4 facilities. The adjusted relative risk (RR) for confirmed outbreaks was 0.82 (95% CI, 0.71-0.96). In 2020-2021, confirmed outbreaks were rare (16 vs 15), and no significant differences were observed. Coronavirus disease 2019 outbreak risk did not differ between groups in either season. Conclusions: RIV4 reduced influenza outbreak occurrence in US nursing homes during a season with moderate influenza activity in older adults. No differences were observed during the low-circulation 2020-2021 season. These findings suggest that recombinant influenza vaccines may provide clinically meaningful facility-level benefits in long-term care settings during seasons with substantial influenza circulation.
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