Many efforts are being made to develop a cure for Alzheimer’s disease. But until today, many promising treatments in animals have subsequently failed in clinical trials. Regarding the progress of vaccines, they are very slow. But several studies suggest that part of the cure may have been under our noses for decades in the form of the flu vaccine.
Rates of Alzheimer’s disease and other forms of dementia are increasing as populations age in high- and middle-income countries. Since advances like vaccination are one of the reasons older people live long enough to develop dementia, one might think that being vaccinated is linked to a higher risk of Alzheimer’s disease.
Yet one study found the opposite, that vaccination is linked to lower rates of Alzheimer’s disease in later years.
Other smaller-scale studies have found something similar, but the results are so startling that analyzes were done on a much larger sample. The findings were later confirmed in the medical journal Journal of Alzheimer’s Disease.
The study, which was carried out two years after UTHealth Houston researchers discovered a possible link between the flu vaccine and lower risk of Alzheimer’s disease, compared nearly 936,000 people over 65 years old who had been vaccinated against the seasonal flu between 2009 and 2015.
Four years later, 5.1% of vaccinated people had developed Alzheimer’s disease, but this figure was 8.5% among unvaccinated people. The study results reveal that people who received at least one flu shot were 40% less likely than their unvaccinated peers to develop Alzheimer’s disease over a four-year period.
However, in the absence of confirmation of a causal chain, we cannot exclude the possibility that another factor is responsible.
It remains to be seen whether vaccination really protects the brain or whether an aggravating factor is responsible. Could a pre-diagnosis symptom of Alzheimer’s disease be resistance to getting shots or being too disorganized to go to the doctor?
The authors tried to solve this problem by comparing patients in the two groups to be as similar as possible in terms of demographics, use of other drugs and other conditions.
According to the study’s lead author, Professor Paul Schulz of the University of Texas, “Since there is evidence that several vaccines can protect against Alzheimer’s disease, we believe it is not a question of a specific effect of the flu vaccine”.
“Instead, we believe that the immune system is complex and that certain alterations, such as pneumonia, can activate it in a way that worsens Alzheimer’s disease. But other things that activate the immune system may do so in a different way, one that protects against Alzheimer’s disease. Obviously, we have more to learn about how the immune system worsens or improves outcomes in this disease.”
This interpretation is supported by the fact that some of the other vaccines that appear protective are usually given much earlier in life.
Adults receiving booster shots for tetanus, diphtheria and whooping cough, for example, also appear to have a lower risk of getting Alzheimer’s disease.
The researchers conducted the study over a period that allowed them to test whether annual vaccinations are more protective than a single injection at first. Unsurprisingly, this appears to be the case, and the benefits fade over the four-year period if patients do not get vaccinated every year.
However, not enough time has passed to test whether vaccination against COVID-19 also protects against Alzheimer’s disease.
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