Researchers in the US have found that getting a flu vaccine in the past four years lessens an individual’s risk of developing Alzheimer’s disease. They caution that the underlying mechanisms behind this process will likely require further study.

A new study from University of Texas Health Houston reveals that individuals who received at least one influenza vaccine were 40 percent less likely than their non-vaccinated peers to develop Alzheimer’s disease over the course of four years.

The research was led by first author Avram S. Bukhbinder, MD, a recent alumnus of the McGovern Medical School at UTHealth Houston, and senior author Paul E. Schulz, MD, the Rick Mc Cord Professor in Neurology at McGovern Medical School.

The authors used a large nationwide sample of US adults aged 65 and older to compare the risk of Alzheimer’s disease incidence between patients with and without prior flu vaccination.

The research has been published online in an early version in the August 2 issue of the Journal of Alzheimer’s Disease.

“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 Bukhbinder, who is still part of Schulz’s research team while in his first year of residency with the Division of Child Neurology at Massachusetts General Hospital.

“Future research should assess whether flu vaccination is also associated with the rate of symptom progression in patients who already have Alzheimer’s dementia.”

Two years earlier, UTHealth Houston researchers had found a possible correlation between the flu vaccine and reduced risk of Alzheimer’s disease. The new study builds on this previous research and samples a much larger group of patients –– 935,887 vaccinated and 935,887 non-vaccinated seniors.

The patients were followed up for four years – about 5.1 percent of flu-vaccinated patients had developed Alzheimer’s disease, compared to 8.5 percent of non-vaccinated patients.

Bukhbinder and Schulz suggest that these results emphasize the strong protective effect of the flu vaccine against Alzheimer’s disease. They caution, however, that the underlying mechanisms behind this process will likely 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 Schulz, who is also the Umphrey Family Professor in Neurodegenerative Diseases and director of the Neurocognitive Disorders Center at McGovern Medical School.

“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.”

Alzheimer’s DIsease International puts the number of people in the world living with dementia at over 55 million. “The number of people affected is set to rise to 139 million by 2050, with the greatest increases in low and middle income countries,” its website notes.

The UK’s National Health Service notes that Alzheimer’s disease, the most common form of dementia, “is most common in people over the age of 65.” The NHS says the risk of Alzheimer’s disease and other types of dementia “increases with age, affecting an estimated 1 in 14 people over the age of 65 and 1 in every 6 people over the age of 80.”

Quoting an earlier study, the CDC says that “In 2020, as many as 5.8 million Americans were living with Alzheimer’s disease.”

The current study points out that “Prevention or attenuation of microbe-related inflammation may therefore represent a rational strategy to delay or reduce the risk of neurodegenerative disease,” adding that “Consistent with this hypothesis, studies have found a decreased risk of dementia associated with prior exposure to various adulthood vaccinations, including those for tetanus, diphtheria, pertussis (Tdap); poliomyelitis; tuberculosis; herpes zoster (ie, shingles); and influenza.”

Bukhbinder said it will be worth investigating whether a similar association between Covid-19 vaccination and the risk of Alzheimer’s disease exists as more passes since the introduction of the Covid-19 vaccines and longer follow-up data become available.

Source: TRTWorld and agencies