A study of 26 million Medicare recipients has linked yearly influenza vaccination with lowered mortality — except in those who required a skilled nursing facility stay. The results suggest that vaccines alone are not enough to prevent deadly flu cases in long-term care settings, investigators contend.

Investigators used Centers for Medicare & Medicaid Services data on vaccination status and timing during the 2017–2018 flu season to estimate the association between flu shot receipt and relative risk of death. They looked at beneficiary groups including those aged 85 and older; those who sought and obtained an annual preventative care/wellness visit; and beneficiaries who did and did not require nursing home care in the month prior to the vaccination window.

Among all groups, people who were vaccinated had a lower risk of dying from any cause except for the group that received nursing home care in the month prior to the vaccination window, Jeffrey A. Kelmanh, M.D., chief medical officer for CMS’s Center for Medicare, reported.

It is possible that residents’ relatively high risk of dying from any cause erased any positive effect of vaccination on mortality. But there may be other explanations for this finding, Kelmanh and colleagues proposed.  

It is possible that “vaccines fail to elicit an immune response sufficient to prevent infection in this population,” they wrote. “The distinction is important because even if the vaccine does not prevent development of the virus in one resident, immunization may in fact reduce spread of the virus to other nursing home residents who are not vaccinated.”

The policy of vaccinating nursing home residents against flu should continue, they added. But the goal of preventing facility influenza outbreaks “should not rely primarily upon vaccine effectiveness,” they added. “Alternative countermeasures to prevent transmission should remain.”

Currently, U.S. flu case counts remain low in the United States, with infections accounting for only 2.2% of visits to a healthcare provider in the week ending Nov. 20. Only 0.2% of long-term care facilities, meanwhile, reported positive flu tests among residents in the same week.

Full findings were published in the journal Vaccine.