Vaccines Linked to Lower Dementia Risk in Multiple Studies

Recent research has examined the association between adult vaccinations and reduced risk of dementia, focusing on several commonly recommended vaccines for older adults.

Analysis of observational studies has identified links between vaccination against herpes zoster, influenza, pneumococcus, Tdap, and RSV and lower rates of dementia or Alzheimer’s disease among adults aged 50 and above. These findings have emerged from both large-scale systematic reviews and specific population studies in different countries.

A systematic review and meta-analysis covering more than 104 million adults aged 50 or older reported that those who received vaccines for herpes zoster, influenza, pneumococcus, or Tdap experienced lower rates of dementia and Alzheimer’s disease compared to those who did not receive these vaccines. The review included 21 observational studies and assessed risk ratios for each vaccine type.

In Wales, a natural experiment in 2013 involving the shingles vaccine Zostavax found that individuals eligible for the vaccine had a 20 percent lower incidence of dementia over a seven-year period compared to those just outside the eligibility criteria. Other studies have also linked the shingles vaccine to reduced risk of mild cognitive impairment and lower mortality from dementia over nine years among those already diagnosed.

What the numbers show

• Systematic review included over 104 million adults aged 50 and older
• Shingles vaccine eligibility in Wales linked to 20% lower dementia incidence over 7 years
• RSV vaccine Arexvy associated with 29% reduction in dementia diagnoses over 18 months
• Herpes zoster vaccine linked to risk ratio of 0.76 for any dementia
• Pneumococcal vaccine associated with risk ratio of 0.64 for Alzheimer’s disease

In the United States, a cohort study involving more than 430,000 adults found that those who received the RSV vaccine Arexvy, which contains the AS01 adjuvant, had a 29 percent lower rate of dementia diagnoses over the following 18 months compared to those who received the flu vaccine. These results add to the body of evidence suggesting a potential association between certain vaccines and lower dementia risk in older populations.

Additional observational studies have reported that shingles vaccination may also be associated with reduced risks of heart attack, stroke, blood clots, vascular dementia, and overall mortality. These findings suggest that the benefits of adult vaccination could extend beyond the prevention of specific infectious diseases.

Most of the evidence connecting vaccines to lower dementia risk comes from observational studies. Researchers note that such studies cannot establish direct causation and may be influenced by factors like healthy-volunteer bias, where individuals who choose to be vaccinated may differ in important ways from those who do not.

According to researchers, while the associations between vaccination and reduced dementia risk are strong in observational data, current evidence does not confirm a cause-and-effect relationship. Ongoing research is needed to clarify the mechanisms and to determine whether the observed associations reflect direct effects of vaccines or other factors.

* This article is based on publicly available information at the time of writing.