Does the flu shot protect against Alzheimer’s dementia?

When there is currently talk of vaccinations in Germany, it is mainly about vaccination skepticism, possible risks and the sluggish vaccination campaign against Covid-19. It is hardly seen that vaccinations – especially those with live vaccines – train the immune system as a whole and thus possibly draw attention to other abuses in the body. The BCG vaccination against tuberculosis, for example, protects against further respiratory infections and was – like the vaccination against measles, mumps, rubella – also discussed as protection against a severe course of Covid-19.

A possible additional benefit that makes you sit up and take notice is now also available for the flu vaccination. Several studies suggest that it reduces the risk of Alzheimer’s dementia. The earlier people in the sixth decade of life get vaccinated and the more regularly they do it, the greater the benefit could be. The most recent study is from Jeffrey Scherrer of Saint Louis University and colleagues and ist in the journal a few days ago Vaccine appeared. The scientists evaluated the medical records of 120,000 mostly male U.S. veterans, most of whom were white.

After that, the risk of illness drops by twelve percent through regular flu vaccinations, but only if vaccinated at least six times over the course of six to seven years. “This effect is not insignificant,” writes Richard Dodel from the University of Duisburg-Essen in a statement by the German Society for Neurology. “With around 330,000 new cases of dementia in Germany every year, regular flu vaccinations could save almost 40,000 people from being diagnosed with dementia every year.”

Figures were also given at the international conference of the American Alzheimer’s Association last year. Albert Amran of the University of Texas Health Science Center at Houston and his colleagues reported a 17 percent decrease in disease risk after a single vaccination and a further 13 percent decrease in annual vaccinations. Apparently, other vaccinations also reduce the risk of Alzheimer’s dementia. Scherrer and his colleagues also see a positive effect in the vaccination against tetanus, diphtheria and whooping cough. Svetlana Ukraintseva from Duke University sees effects in the pneumococcal vaccination. The latter protects against bacterial pneumonia.

Alzheimer’s dementia is also an immune failure

But what informative value do these studies have? None of these have a high quality design. In all of them, medical records were subsequently evaluated. Such backward-looking studies only show that two events are correlated, not that one is the cause of the other. All of the study authors tried to take into account distorting influences such as a low level of education, little exercise and long-term smoking, but that does not change the fact that correlations have no evidential value.

Why are these results still remarkable? On the one hand, the prospect of being able to arm oneself against Alzheimer’s dementia with a flu vaccination would be impressive. If those little spades were to reduce the risk of pathological forgetting, it would indeed be a landslide in dementia prevention. On the other hand, there is also a plausible explanation of how this effect could come about, which is supported by animal experiments.

Alzheimer’s dementia – this is now clear – is always also an immune failure. Therefore, vaccination-related training of the immune system, during which many messenger substances are released, could put the body’s defenses on a heightened level of alert. This also affects the so-called microglia cells in the brain. These belong to the innate immune system and report the dangers they encounter in the brain. Microglia cells are also part of the cleaning system with which the brain is freed from all kinds of cell debris and protein waste during sleep. If this cleaning system fails because the microglia cells capitulate, the protein waste builds up and becomes a problem. The training with the flu vaccination could give the microglia cells the decisive kick so that they participate again in the elimination of the protein waste. This has been shown in experiments with Alzheimer’s mice.

At the moment, however, this finding is only one piece of the puzzle that may not give a picture at all. Scherrer and his colleagues also cite other explanations for the connection between the flu vaccination and the decrease in the risk of developing Alzheimer’s disease: One of them is that people who receive regular vaccinations live healthier lives and therefore have a lower risk of developing the disease. Another possible explanation is that people with the onset of dementia go to the doctor more often and are also vaccinated against the flu. If both of these explanations are true, the interesting hypothesis of the usefulness of flu vaccination in dementia prevention is over.

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