In a cohort study of more than 9,000 older adults, receiving a single influenza vaccination was associated with a 17% lower prevalence of Alzheimer’s disease compared with not receiving the vaccine. In addition, for those who were vaccinated more than once over the years, there was an additional 13% reduction in Alzheimer’s disease incidence.
In another study, which included more than 5,000 older participants, being vaccinated against pneumonia between the ages of 65 and 75 reduced the risk of developing Alzheimer’s disease by 30%.
The subject of vaccines “is obviously very topical with the COVID-19 pandemic,” said Rebecca M. Edelmayer, PhD, director of scientific engagement for the Alzheimer’s Association. “While these are very preliminary data, these studies do suggest that with vaccination against both respiratory illnesses, there is the potential to lower risk for developing cognitive decline and dementia,” said Dr. Edelmayer, who was not involved in the research.
The findings of both studies were presented at the virtual annual meeting of the Alzheimer’s Association International Conference.
Lower Alzheimer’s disease prevalence
The influenza vaccine study was presented by Albert Amran, a fourth-year medical student at McGovern Medical School at the University of Texas Health Science Center at Houston. The researchers used electronic health record data to create a propensity-matched cohort of 9,066 vaccinated and unvaccinated adults ages 60 and older.
Influenza vaccination, increased frequency of administration, and younger age at time of vaccination were all associated with reduced incidence of Alzheimer’s disease, Mr. Amran reported.
Being vaccinated for influenza was significantly linked to a lower prevalence of Alzheimer’s disease (odds ratio [OR], 0.83; P < .0001) in comparison with not being vaccinated. Receiving more than one vaccination over the years was associated with an additional reduction in AD incidence (OR, 0.87; P = .0342). The protection appeared to be strongest for those who received their first vaccination at a younger age, for example, at age 60 versus 70.
Mr. Amran and research colleagues have two theories as to why influenza vaccination may protect the brain.
One is that vaccination may aid the immune system as people age. “As people get older, their immune systems become less able to control infection. We’ve seen this with the ongoing pandemic, with older people at much higher risk for dying. Giving people the vaccine once a year may help keep the immune system in shape,” Mr. Amran said.
Another theory is that the prevention of influenza itself may be relevant. “Flu infections can be extremely deadly in older patients. Maybe the results of our study will give another reason for people to get vaccinated,” Mr. Amran said.
Pneumonia vaccine
The other study was presented by Svetlana Ukraintseva, PhD, of Duke University, Durham, N.C.
Dr. Ukraintseva and colleagues investigated associations between pneumococcal vaccine, with and without an accompanying influenza vaccine, and the risk for Alzheimer’s disease among 5,146 participants in the Cardiovascular Health Study. Covariates included sex, race, birth cohort, education, smoking, and a known genetic risk factor for Alzheimer’s disease: the rs2075650 G allele in the TOMM40 gene.
In a logistic model with all covariates, vaccination against pneumonia between ages 65 and 75 was significantly associated with reduced risk of developing AD (OR, 0.70; P < .04). The largest reduction in Alzheimer’s disease risk (OR, 0.62; P < .04) was among those vaccinated against pneumonia who were noncarriers of the rs2075650 G allele.
Total number of vaccinations against pneumonia and influenza between ages 65 and 75 was also associated with a lower risk for Alzheimer’s disease (OR, 0.88; P < .01). However, the effect was not evident for the influenza vaccination alone.
“The fact that very different pathogens – viral, bacterial, fungal – have been linked to Alzheimer’s disease indicates a possibility that compromised host immunity may play a role in Alzheimer’s disease through increasing overall brain’s vulnerability to various microbes,” said Dr. Ukraintseva.
The current findings support further investigation of pneumococcal vaccine as a “reasonable candidate for repurposing in personalized AD prevention,” she noted. “These results also support the important role of boosting overall immune robustness/resilience in preventing Alzheimer’s disease,” Dr. Ukraintseva added.
Her group is currently working on confirming the findings in another population.