TOPLINE

Nursing homes using recombinant quadrivalent influenza vaccine (RIV4) experienced 18% fewer laboratory-confirmed influenza outbreaks compared with facilities using standard-dose egg-based inactivated quadrivalent influenza vaccine (IIV4) during the 2019-2020 season in a cluster-randomized trial. However, no differences in outbreak rates were seen between vaccine groups during the 2020-2021 season, when influenza circulation was historically low.

METHODOLOGY

• Researchers conducted a pragmatic cluster-randomized trial across two influenza seasons to determine whether recombinant influenza vaccine reduced transmission in long-term care settings. 
• They enrolled 965 Medicare-certified nursing homes in 2019-2020 and 1023 facilities in 2020-2021. Eligible facilities had at least 50 long-stay residents with 80% aged older than 65 years or at least 70 long-stay residents older than 65 years comprising at least 45% of total beds.
• Facilities were randomly assigned to provide either RIV4 (containing 45 µg per antigen) or IIV4 (containing 15 µg per antigen) to residents and staff.
• The study outcome was facility-reported influenza outbreaks, defined as laboratory-confirmed outbreaks (≥ 1 laboratory-confirmed cases with other respiratory illness cases in a unit) or suspected outbreaks (≥ 2 influenza-like illness cases), assessed through monthly logs.

TAKEAWAY

• In the 2019-2020 season, facilities assigned to RIV4 had fewer laboratory-confirmed influenza outbreaks than IIV4 facilities (36.6% vs 44.5%; adjusted relative risk [RR], 0.82; 95% CI, 0.71-0.96).
• Suspected influenza outbreaks were also reduced with recombinant vaccine during 2019-2020 (30.6% vs 37.0%; adjusted RR, 0.82; 95% CI, 0.69-0.97).
• During the 2020-2021 season, confirmed influenza outbreaks were rare in both groups (3.1% with RIV4 vs 2.9% with IIV4), with no significant differences (adjusted RR, 1.04; 95% CI, 0.47-2.00).
• The risk for COVID outbreak did not differ between the vaccine assignment groups in either season (2019-2020: adjusted RR, 1.09; 95% CI, 0.90-1.30; 2020-2021: adjusted RR, 0.97; 95% CI, 0.71-1.25).

IN PRACTICE

"These findings suggest that enhanced influenza vaccines may provide meaningful facility-level benefits in typical influenza seasons by reducing outbreak occurrence, even when resident-level clinical outcomes show limited differences. Continued evaluation of enhanced vaccines in long-term care settings remains important as influenza epidemiology evolves and multiple vaccine formulations become available," the authors of the study concluded.

SOURCE

The study was led by Kevin W. McConeghy, PharmD, PhD, MS, Transformative Health Systems Research to Improve Veteran Equity and Independence Center of Innovation, Veterans Affairs Providence Healthcare System in Providence, Rhode Island. It was published online on August 27, 2026, in Open Forum Infectious Diseases.

LIMITATIONS

Outbreak data were facility-reported and may have been misclassified. The COVID pandemic changed infection control and reporting patterns. The findings came from US community nursing homes and may not be generalizable to other settings or seasons.

DISCLOSURES

The study was supported by an investigator-initiated research award from Sanofi Pasteur. Multiple authors reported receiving research funding, consulting fees, and speaker fees from pharmaceutical companies, including Genentech, GlaxoSmithKline, Moderna, Pfizer, Sanofi, and Seqirus. Full disclosures are reported in the original article.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.