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Flu and pneumonia vaccinations were linked to reduced risk of Alzheimer's disease, research from the virtual Alzheimer's Association International Conference (AAIC) suggested.

People who were vaccinated against pneumonia when they were ages 65 to 75 years had nearly 40% less risk of Alzheimer's disease depending on their genetic profile, reported Svetlana Ukraintseva, PhD, of Duke University in Durham, North Carolina, and colleagues.

And having at least one influenza vaccination was associated with a 17% reduction in Alzheimer's prevalence, an analysis by Albert Amran, a medical student at the University of Texas Health Science Center at Houston, and colleagues showed.

"The fact that very different pathogens -- viral, bacterial, fungal -- have been linked to Alzheimer's disease suggests a possibility that a compromised host immunity may play role in Alzheimer's through increased overall brain's vulnerability to microbes," Ukraintseva said.

"Some vaccines show beneficial off-target effects on health that span beyond the protection against specific disease," she told 番茄社区. "This could be because they may improve immunity on a broad scale."

In their report, Ukraintseva and colleagues looked at links between Alzheimer's and pneumococcal vaccination, with and without an accompanying seasonal flu shot, in 5,146 participants, ages 65 and older, from the . "We decided to take into account a strong genetic risk factor for Alzheimer's disease -- G allele of rs2075650 [in the TOMM40 gene] -- linked to NECTIN2 gene, which is involved in blood-brain barrier permeability and vulnerability to infection," she said.

Being vaccinated against pneumonia between ages 65 and 75 was tied to reduced risk of Alzheimer's afterwards (OR 0.70, P <0.04), after adjusting for covariates that included sex, race, birth cohort, education, smoking, and rs2075650.

A larger reduction in Alzheimer's risk (OR 0.62, P <0.04) emerged in people vaccinated against pneumonia who were non-carriers of the rs2075650 G allele. "This means that adult vaccination against pneumonia may reduce Alzheimer's risk depending on individual genotype, which supports personalized prevention of Alzheimer's disease," Ukraintseva noted.

Total count of pneumonia and flu vaccinations between ages 65 and 75 also correlated with a lower risk of Alzheimer's later in life (OR 0.88, P <0.01), but this effect was not seen for flu shots alone.

Relationships between flu vaccination and Alzheimer's disease appeared in other research presented at AAIC. In an observational study, Amran and colleagues evaluated a propensity-matched set of 9,066 vaccinated and unvaccinated people, ages 60 and older, with Alzheimer's disease ICD9 codes, culled from the

In this group, having one documented flu vaccination was associated with a lower prevalence of Alzheimer's (OR 0.83, P<0.0001), compared with not receiving the vaccine. Frequency of flu shots also was associated with reduced Alzheimer's onset (OR 0.87, P=0.0342).

Links between flu vaccination and Alzheimer's were strongest for people who had their first vaccine at a younger age: those who received their first documented flu shot at age 60 benefitted more than those who received their first shot at age 70.

"Getting a flu shot is an example of a healthy behavior," noted Dallas Anderson, PhD, MPH, of the National Institute on Aging in Bethesda, Maryland, who wasn't involved with either study.

"There may be health effects beyond preventing the flu. For example, there has been some research looking at reduced risk for stroke and stroke hospitalization. It makes sense to also look at reduced risk for dementia," he said in an interview with 番茄社区.

"Observational studies can never show definitively that getting flu shots will prevent Alzheimer's disease or dementia. The evidence will be suggestive at best," Anderson continued. "Is it the flu shot itself that's important? Or is it key differences between those who opt for flu shots and those who don't? Studies need to account for those differences."

Besides these limitations, the research was constrained by the underlying data: clinical codes may reflect other dementia, not just Alzheimer's disease. In both studies, unmeasured variables may have influenced results.

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