Adjuvanted Flu Vaccine Outperforms Non-Adjuvanted Vaccines in Nursing Home Residents

Stefan Gravenstein, MD, PhD

Adjuvanted trivalent flu vaccine appears to better-protect elderly patients in nursing homes from influenza outbreaks when compared to non-adjuvanted vaccines, according to a new study.

Corresponding author Stefan Gravenstein, MD, PhD, of the Warren Alpert Medical School of Brown University, and colleagues, wanted to learn more about how best to prevent deadly outbreaks of influenza in nursing homes. Specifically, the investigators sought to understand whether adjuvanted trivalent influenza vaccine (aTIV) would provide a meaningful benefit versus non-adjuvanted trivalent vaccine (TIV).

An adjuvant is a substance added to a vaccine to boost its efficacy. In the current study, the investigators used the Fluad vaccine, which contains the adjuvant MF59.

Though the coronavirus disease 2019 (COVID-19) pandemic has been the dominant public health concern for the past 13 months, Gravenstein and colleagues noted that influenza is a perennial threat, particularly to elderly patients living in close quarters, such as in nursing homes and long-term care facilities.

“Influenza outbreaks in nursing homes pose a threat to frail residents and occur even in vaccinated populations,” Gravenstein and colleagues noted.

The US Centers for Disease Control and Prevention (CDC) estimates for the 2019-2020 influenza season showed that while only about 5% of influenza cases in the US occurred in a patient over the age of 65, that age cohort made up nearly half of the 404,646 hospitalizations for influenza. Those aged 65 and older comprised nearly two-thirds of the 21,909 estimated flu deaths in the US occurred in elderly patients (13,673 deaths).

The push to boost flu vaccinations in nursing homes is not only related to the high risk of death; it also is an important step because a high number of hospitalizations related to influenza could exacerbate the already stretched capacity of healthcare providers in the United States due to the pandemic.

The new study is based on data from the 2016-2017 flu season. Graventstein and colleagues selected 823 nursing homes for their study, 777 of which reported information related to influenza outbreaks. Those nursing homes were randomized into aTIV and TIV groups, with 387 using adjuvanted vaccines, and the remaining 390 using non-adjuvanted vaccines.

The investigators used CDC definitions for suspected outbreaks and outbreaks with laboratory-confirmed cases to evaluate the nursing homes’ flu seasons, and then adjusted the data for facility-level vaccination rates and the characteristics of the facilities’ residents.

A total of 133 outbreaks were reported at the nursing homes distributing aTIV, versus 162 outbreaks at the nursing homes in the TIV cohort. Most of the outbreaks (115 and 140, respectively) were laboratory confirmed. Using those data, the investigators calculated that the aTIV group had a 17% reduction in suspected and laboratory-confirmed influenza outbreaks. A covariate adjustment further boosted the estimated reduction in outbreaks to 21% for suspected outbreaks and 22% for laboratory-confirmed outbreaks.

Trivalent Fluad is approved by the US Food and Drug Administration (FDA) for patients 65 years and older. A quadrivalent version of Fluad was approved last year, making it the only adjuvanted quadrivalent flu vaccine available in the US.

The study, “Adjuvanted influenza vaccine and influenza outbreaks in U.S. nursing homes: Results from a pragmatic cluster-randomized clinical trial,” was published online in Clinical Infectious Diseases.