Editor's Note
Aging and Health
Intensive Chemoprophylaxis for Nursing Home Influenza Outbreaks—The Race Against Transmission
Justin J. Choi, Sharon K. Inouye, Lona Mody
JAMA Intern Med Published Online: March 30, 2026
doi: 10.1001/jamainternmed.2026.0409
Influenza outbreaks are common and lead to morbidity in nursing home (NH) residents. To limit transmission, clinical guidelines from the US Centers for Disease Control and Prevention and the Infectious Diseases Society of America recommend prompt oseltamivir chemoprophylaxis for all exposed residents, even if asymptomatic.1,2However, whether there is a threshold of proportion of residents who should receive postexposure prophylaxis to reduce serious complications such as hospitalization has not been studied. Of course, a randomized clinical trial (ideally a cluster-randomized trial) would be most desirable. However, conducting a cluster-randomized trial to answer this question would be logistically and ethically difficult as influenza outbreaks require an immediate response under evolving conditions that may outpace the implementation of such a study protocol for a known effective treatment.
In this issue of JAMA Internal Medicine, Silva et al3 address this gap by using a sequential target trial and randomize-censor-weight approach to emulate a cluster-randomized trial of oseltamivir chemoprophylaxis in NHs. This approach accounts for treatment strategies that unfold over time at the discretion of NHs, censoring facilities that deviate from their assigned strategy while using statistical adjustments to control for the fact that NHs that deviate might differ fundamentally from those that adhere to their assigned strategy. In analyzing more than 400 outbreaks across 318 NHs, the authors found a substantial reduction in 14-day hospitalization risk when at least 70% of eligible residents received oseltamivir within 2 days of outbreak detection. Alternative coverage thresholds of 60% or more and 80% or more were also associated with reductions in hospitalization risk. These results are informative as facilities often struggle to achieve complete compliance with oseltamivir prophylaxis.
However, these positive results should be viewed with a degree of caution, particularly with potential unmeasured confounding. NHs that achieve rapid coverage of residents who were not ill within 2 days of an outbreak are likely different from those that do not in ways that may meaningfully influence the observed reduction in hospitalization risk. For example, facilities that institute immediate prophylaxis may also have better staffing, more staff training in infection control and other areas, up-to-date policies on the use of personal protective equipment, and a well-resourced infection prevention team that can all influence hospitalization risk and are not captured by electronic health record data.
Limitations notwithstanding, these findings provide actionable evidence to guide infection control staff and medical directors at NHs in making timely and effective decisions around chemoprophylaxis during influenza outbreaks. While awaiting a definitive trial, this large-scale target trial emulation may provide the best available evidence to date to support widespread implementation of this timely and important approach to limit the substantial morbidity and mortality associated with influenza outbreaks in nursing homes.
