People who received at least one influenza vaccine were 40 per cent less likely than their non-vaccinated peers to develop Alzheimer's disease over the course of four years, according to a new study.

Research from the University of Texas Health Science Center, Houston compared the risk of Alzheimer's disease incidence between patients with and without prior flu vaccination in a large nationwide sample of US adults aged 65 and older.

"We found that flu vaccination in older adults reduces the risk of developing Alzheimer's disease for several years. The strength of this protective effect increased with the number of years that a person received an annual flu vaccine -- in other words, the rate of developing Alzheimer's was lowest among those who consistently received the flu vaccine every year," said Avram S. Bukhbinder, from the varsity.

"Future research should assess whether flu vaccination is also associated with the rate of symptom progression in patients who already have Alzheimer's dementia," Bukhbinder added. The study included 935,887 flu-vaccinated patients and 935,887 non-vaccinated patients.

During four-year follow-up appointments, about 5.1 per cent of flu-vaccinated patients were found to have developed Alzheimer's disease. Meanwhile, 8.5 per cent of unvaccinated patients had developed Alzheimer's disease during follow-up.

These results underscore the strong protective effect of the flu vaccine against Alzheimer's disease, according to Bukhbinder and his associates. However, the underlying mechanisms behind this process require further study.

"Since there is evidence that several vaccines may protect from Alzheimer's disease, we are thinking that it isn't a specific effect of the flu vaccine," said Paul. E. b Schulz, Professor at the varsity.

"Instead, we believe that the immune system is complex, and some alterations, such as pneumonia, may activate it in a way that makes Alzheimer's disease worse.

But other things that activate the immune system may do so in a different way -- one that protects from Alzheimer's disease. Clearly, we have more to learn about how the immune system worsens or improves outcomes in this disease," he said.

Past studies have found a decreased risk of dementia associated with prior exposure to various adulthood vaccinations, including those for tetanus, polio, and herpes, in addition to the flu vaccine and others.

Additionally, as more time passes since the introduction of the COVID-19 vaccine and longer follow-up data become available, Bukhbinder said it will be worth investigating whether a similar association exists between COVID-19 vaccination and the risk of Alzheimer's disease.