Summary: Older adults who received at least one flu vaccination were 40% less likely to develop Alzheimer’s disease over the course of a four-year follow-up than their peers who did not receive a vaccine.
Source: UT Houston
People who received at least one influenza vaccine were 40% less likely than their non-vaccinated peers to develop Alzheimer’s disease over the course of four years, according to a new study from UTHealth Houston.
Research led by first author Avram S. Bukhbinder, MD, a recent alumnus of McGovern Medical School at UTHealth Houston, and senior author Paul. E. Schulz, MD, the Rick McCord Professor in Neurology at McGovern Medical School, compared the risk of Alzheimer’s disease incidence between patients with and without prior flu vaccination in a large nationwide sample of U.S. adults aged 65 and older.
An early online version of the paper detailing the findings is available in advance of its publication in the Aug. 2 issue of the Journal of Alzheimer’s Disease.
“We found that flu vaccination in older adults reduces the risk of developing Alzheimer’s disease for several years. The strength of this protective effect increased with the number of years that a person received an annual flu vaccine—in other words, the rate of developing Alzheimer’s was lowest among those who consistently received the flu vaccine every year,” said Bukhbinder, who is still part of Schulz’s research team while in his first year of residency with the Division of Child Neurology at Massachusetts General Hospital.
“Future research should assess whether flu vaccination is also associated with the rate of symptom progression in patients who already have Alzheimer’s dementia.”
The study—which comes two years after UTHealth Houston researchers found a possible link between the flu vaccine and reduced risk of Alzheimer’s disease—analyzed a much larger sample than previous research, including 935,887 flu-vaccinated patients and 935,887 non-vaccinated patients.
During four-year follow-up appointments, about 5.1% of flu-vaccinated patients were found to have developed Alzheimer’s disease. Meanwhile, 8.5% of non-vaccinated patients had developed Alzheimer’s disease during follow-up.
These results underscore the strong protective effect of the flu vaccine against Alzheimer’s disease, according to Bukhbinder and Schulz. However, the underlying mechanisms behind this process require further study.
“Since there is evidence that several vaccines may protect from Alzheimer’s disease, we are thinking that it isn’t a specific effect of the flu vaccine,” said Schulz, who is also the Umphrey Family Professor in Neurodegenerative Diseases and director of the Neurocognitive Disorders Center at McGovern Medical School.
“Instead, we believe that the immune system is complex, and some alterations, such as pneumonia, may activate it in a way that makes Alzheimer’s disease worse. But other things that activate the immune system may do so in a different way—one that protects from Alzheimer’s disease. Clearly, we have more to learn about how the immune system worsens or improves outcomes in this disease.”
Alzheimer’s disease affects more than 6 million people living in the U.S., with the number of affected individuals growing due to the nation’s aging population. Past studies have found a decreased risk of dementia associated with prior exposure to various adulthood vaccinations, including those for tetanus, polio, and herpes, in addition to the flu vaccine and others.
Additionally, as more time passes since the introduction of the COVID-19 vaccine and longer follow-up data becomes available, Bukhbinder said it will be worth investigating whether a similar association exists between COVID-19 vaccination and the risk of Alzheimer’s disease.
About this vaccinations and Alzheimer’s disease research news
Original Research: Open access.
“Risk of Alzheimer’s Disease Following Influenza Vaccination: A Claims-Based Cohort Study Using Propensity Score Matching” by Avram S. Bukhbinder et al. Journal of Alzheimer’s Disease
Risk of Alzheimer’s Disease Following Influenza Vaccination: A Claims-Based Cohort Study Using Propensity Score Matching
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 characterized.
To compare the risk of incident AD between patients with and without prior influenza vaccination in a large US claims database.
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.
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.
This study demonstrates that influenza vaccination is associated with reduced AD risk in a nationwide sample of US adults aged 65 and older.
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