What Effect Does the Influenza Vaccine Have on Alzheimer Disease Risk?

Influenza vaccination reduced the risk for Alzheimer disease (AD) among adults aged 65 years and older, according to study findings published in the Journal of Alzheimer’s Disease.

Mounting evidence suggests that systemic immune responses may affect AD risk and/or progression and a range of microorganisms and infectious diseases have been associated with AD risk. Previous studies have linked influenza vaccination with reduced AD risk among veterans and individuals with chronic health conditions.

The researchers of the current study hypothesized that the association between vaccination and AD risk is likely similar among the general population.

Researchers at the John P and Katherine G McGovern Medical School at UTHealth sourced data for this study from the Optum® Clinformatics® Data Mart. This database contains medical, pharmacy, and administrative claims from individuals with private insurance or Medicare Advantage Part D in the United States. Individuals who were aged 65 years and older as of September 2015 were evaluated for the number of annual influenza vaccines received between September 2009 and August 2015 and related with AD onset between September 2015 and August 2019 using a propensity matching approach. Incident AD was defined as 2 or more AD-related claims.

Prior to propensity matching, 1,170,868 individuals were unvaccinated and 1,185,611 received a vaccine. The propensity-matched cohorts comprised 935,887 individuals each. At the beginning of the follow-up period, the unvaccinated and vaccinated cohorts were aged mean 73.7 (standard deviation [SD], 6.3) and 73.7 (SD, 6.0) years, 57.0% and 56.8% were women, and 75.6% and 76.6% were White, respectively.

During the follow-up period, there were 79,630 incident AD events in the unvaccinated group and 47,889 in the vaccinated cohort. Vaccination was associated with reduced risk for AD (relative risk [RR], 0.60; 95% CI, 0.59-0.61; absolute risk reduction [ARR], 0.034; 95% CI, 0.033-0.035).

In sensitivity analyses, similar results were observed when nonspecific and senile dementia codes were excluded (RR, 0.65; 95% CI, 0.64-0.66; ARR, 0.016; 95% CI, 0.015-0.017) and when all AD and related dementias were included (RR, 0.60; 95% CI, 0.59-0.61; ARR, 0.033; 95% CI, 0.032-0.034).

The number of influenza vaccines was significantly related with AD risk (subdistribution hazard ratio [sHR], 0.76; 95% CI, 0.74-0.79 per vaccine).

This study may have been limited by not including evidence of influenza infection.

These data indicated that receiving a vaccine for influenza decreased the risk for developing AD over the next 4 years by 40% among individuals aged 65 years and older.

The researchers concluded that “It will be critical for future investigations to clarify which mechanisms underlie the apparent effect of flu vaccination on AD risk, whether age at vaccination moderates the vaccine’s association with AD risk, and whether influenza vaccination also affects rate of progression in patients with MCI [mild cognitive impairment] or AD.”

Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.

Reference

Bukhbinder AS, Ling Y, Hasan O, et al. Risk of Alzheimer’s Disease Following Influenza Vaccination: A Claims-Based Cohort Study Using Propensity Score Matching. J Alzheimers Dis. Published online June 13, 2022. doi:10.3233/JAD-220361