A new study provides more evidence that the influenza vaccination may help protect older adults against Alzheimer's disease (AD).
In a large propensity-matched cohort of older adults, those who had received at least one influenza inoculation were 40% less likely than unvaccinated peers to develop AD over the course of four years.
“Influenza infection can cause serious health complications, particularly in adults 65 and older. Our study’s findings – that vaccination against the flu virus may also reduce the risk of Alzheimer’s dementia for at least a few years ― adds to the already compelling reasons to get the flu vaccine annually,” Dr Avram Bukhbinder, of the McGovern Medical School at the UTHealth, Houston, Texas, told Medscape Medical News.
These findings support earlier work by the same researchers that also suggested a protective effect of flu vaccination on dementia risk.
The latest study was published online in the Journal of Alzheimer’s Disease.
40% Lower Risk
Prior studies have found a lower risk of dementia of any etiology after influenza vaccination in selected populations, including veterans and patients with serious chronic health conditions.
However, the effect of influenza vaccination on AD risk in a general cohort of older US adults has not been characterised.
Bukhbinder and colleagues used claims data to create a propensity-matched cohort of 935,887 influenza-vaccinated and a like number of unvaccinated adults aged 65 and older.
The median age of the people in the matched sample was 73.7 years, and 57% were women. All were free of dementia during the six-year look-back study period.
During median follow-up of 46 months, 47,889 (5.1%) flu-vaccinated adults and 79,630 (8.5%) unvaccinated adults developed AD.
The risk of AD was 40% lower in the vaccinated group (relative risk, 0.60; 95% CI, 0.59 – 0.61). The absolute risk reduction was 0.034 (95% CI, 0.033 – 0.035), corresponding to a number needed to treat of 29.4.
Mechanism unclear
“Our study does not address the mechanism(s) underlying the apparent effect of influenza vaccination on Alzheimer’s risk, but we look forward to future research investigating this important question,” Bukhbinder said.
“One possible mechanism is that, by helping to prevent or mitigate infection with the flu virus and the systemic inflammation that follows such an infection, the flu vaccine helps to decrease the systemic inflammation that may have otherwise occurred,” he explained.
It’s also possible that influenza vaccination may trigger non–influenza-specific changes in the immune system that help to reduce the damage caused by AD pathology, including amyloid plaques and neurofibrillary tangles, he said.
“For example, the influenza vaccine may alter the brain’s immune cells such that they are better at clearing Alzheimer’s pathologies, an effect that has been seen in mice, or it may re-programme these immune cells to respond to Alzheimer’s pathologies in ways that are less likely to damage nearby healthy brain cells, or it may do both,” Bukhbinder noted.
Alzheimer’s expert weighs in
Offering perspective on the study, Heather Snyder, PhD, vice-president of medical and scientific relations for the Alzheimer’s Association, said: “This study suggests that flu vaccination may be valuable for maintaining cognition and memory as we age. This is even more relevant today in the COVID-19 environment.
“It is too early to tell if getting flu vaccine, on its own, can reduce risk of Alzheimer’s. More research is needed to understand the biological mechanisms behind the results.
“For example, it is possible that people who are getting vaccinated also take better care of their health in other ways, and these things add up to lower risk of Alzheimer’s and other dementias,” she said.
“It is also possible that there are issues related to unequal access and/or vaccine hesitancy and how this may influence the study population and the research results.”
Study details
Risk of Alzheimer’s Disease Following Influenza Vaccination: A Claims-Based Cohort Study Using Propensity Score Matching
Bukhbinder, Avram S; Ling, Yaobinb; Hasan, Omar; Jiang, Xiaoqianb; Kim, Yejinb; Phelps, Kamal N; Schmandt, Rosemarie E; |Amran, Alberta; Coburn, Ryana ; Ramesh, Srivathsana; Xiao, Qianc; Schulz, Paul.
Published in the Journal of Alzheimer’s Disease on 13 June 2022
Abstract
Background
Prior studies have found a reduced risk of dementia of any etiology following influenza vaccination in selected populations, including veterans and patients with serious chronic health conditions. However, the effect of influenza vaccination on Alzheimer’s disease (AD) risk in a general cohort of older US adults has not been characterised.
Objective
To compare the risk of incident AD between patients with and without prior influenza vaccination in a large US claims database.
Methods
Deidentified claims data spanning September 1, 2009 through August 31, 2019 were used. Eligible patients were free of dementia during the 6-year look-back period and≥65 years old by the start of follow-up. Propensity-score matching (PSM) was used to create flu-vaccinated and flu-unvaccinated cohorts with similar baseline demographics, medication usage, and comorbidities. Relative risk (RR) and absolute risk reduction (ARR) were estimated to assess the effect of influenza vaccination on AD risk during the 4-year follow-up.
Results
From the unmatched sample of eligible patients (n = 2,356,479), PSM produced a sample of 935,887 flu–vaccinated-unvaccinated matched pairs. The matched sample was 73.7 (SD, 8.7) years of age and 56.9% female, with median follow-up of 46 (IQR, 29–48) months; 5.1% (n = 47,889) of the flu-vaccinated patients and 8.5% (n = 79,630) of the flu-unvaccinated patients developed AD during follow-up. The RR was 0.60 (95% CI, 0.59–0.61) and ARR was 0.034 (95% CI, 0.033–0.035), corresponding to a number needed to treat of 29.4.
Conclusion
This study demonstrates that influenza vaccination is associated with reduced AD risk in a nationwide sample of US adults aged 65 and older.
Medscape article – More Evidence the Flu Vaccine May Guard Against Alzheimer’s (Open access)
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