tetano
Editor, Senior Moderator
Open Forum Infect Dis
. 2026 Aug 27;13(9)
fag522.
doi: 10.1093/ofid/ofag522. eCollection 2026 Sep.
Kevin W McConeghy 1 2 , H Edward Davidson 3 , Lisa Han 3 , David H Canaday 4 5 , Yasin Abul 6 , Kaleen N Hayes 1 2 , Stefan Gravenstein 1 6
Affiliations
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.
Keywords: influenza; nursing homes; outbreaks; recombinant influenza vaccine.
. 2026 Aug 27;13(9)
fag522.doi: 10.1093/ofid/ofag522. eCollection 2026 Sep.
Recombinant Influenza Vaccine and Influenza Outbreaks in US Nursing Homes: Results From a Pragmatic Cluster-Randomized Clinical Trial
Kevin W McConeghy 1 2 , H Edward Davidson 3 , Lisa Han 3 , David H Canaday 4 5 , Yasin Abul 6 , Kaleen N Hayes 1 2 , Stefan Gravenstein 1 6
Affiliations
- PMID: 42751326
- PMCID: PMC13579472
- DOI: 10.1093/ofid/ofag522
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.
Keywords: influenza; nursing homes; outbreaks; recombinant influenza vaccine.