Up to date with your tetanus shots? What about flu? Or herpes zoster, more comfortably known as shingles? Don’t forget your COVID booster.

At this point, you might be thinking to yourself: I’m heartily sick of vaccines.  Fair enough.

But here’s some motivation to staying up to date with… everything.

A series of studies in the US have found that vaccination against tetanus and diphtheria, shingles, and pneumococcus are all associated with a reduced risk for developing Alzheimer’s disease.

The research began with flu vaccines

The first of these studies was published in 2022. It found that people who received at least one influenza vaccine were 40 per cent less likely to develop Alzheimer’s disease over a four-year follow-up.

That was compared to participants who had not received the vaccination.

This was a big study, from the University of Texas Health Science Center in Housten. 

Researchers analysed existing medical claims data from patients aged 65 years or over and free of dementia.

They created two groups, each consisting of 935,887 patients.

The first group had received the flu vaccine while the second group had not. The groups were matched with regard to baseline demographics, medications and comorbidities.

First author of the study is Dr Avram S. Bukhbinder, a recent alumnus of the medical school. He said, in a prepared statement:

“We found that flu vaccination in older adults reduces the risk of developing Alzheimer’s disease for several years.”

He said 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”.

During four-year follow-up appointments, it was discovered that about 5.1 per cent of flu-vaccinated patients had developed Alzheimer’s disease. Meanwhile, 8.5 per cent of non-vaccinated patients had developed Alzheimer’s disease during follow-up.

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

That raises the tantalizing prospect that vaccinations might slow the progression of symptoms.

The other vaccines

Dr Paul E. Schulz, Professor in Neurology with McGovern Medical School, was senior author of the paper.

With the success of the influenza study, Schulz and his team “were wondering whether the influenza finding was specific to the flu vaccine”.

Or was it possible that similar results could be found with other vaccines?

They conducted retrospective cohort studies in people who’d received the tetanus and diphtheria, shingles or pneumococcal vaccines – and in people who hadn’t been vaccinated against any of these diseases.

Ultimately, they calculated the relative risk and absolute risk reduction for developing Alzheimer’s disease.

(A retrospective cohort study is designed to compare the outcomes of two groups of patients after an exposure.)

The findings were encouraging:

• Patients who received the diphtheria/tetanus vaccine were 30 per cent less likely than their unvaccinated peers to develop Alzheimer’s disease. (7.2 per cent of vaccinated patients versus 10.2 per cent of unvaccinated patients developed the disease.)
• The shingles vaccination Zostavax was associated with a 25 per cent reduced risk of developing Alzheimer’s. (8.1 per cent of vaccinated patients versus 10.7 per cent of unvaccinated patients.)
• For the pneumococcal vaccine, there was an associated 27 per cent reduced risk. (7.92 per cent of vaccinated patients versus 10.9 per cent of unvaccinated patients).For comparison, Schulz said, three new anti-amyloid antibodies used to treat Alzheimer’s have shown they slow disease progression by 25 per cent, 27 per cent, and 35 per cent.

This week, Oxford scientists, in a new study, found that the  recombinant shingles vaccine, Shingrix, which was added to Australia’s National Immunisation Program in November last year, is linked with a larger reduction in risk of dementia Zostravax.

This suggests that, over time, ongoing vaccination research could lead to greater protections against Alzheimer’s.

How do the vaccines work?

Dr Bukhbinder said the reduced risk of Alzheimer’s disease associated with vaccines was likely due to a combination of mechanisms.

One idea is that vaccines may change how the immune system responds to the build-up of toxic proteins that contribute to Alzheimer’s disease.

These are the amyloid beta and tau proteins that collect in the brain, years before Alzheimer’s symptoms.

Bukhbinder said the vaccines might enhance the efficiency of immune cells at clearing these proteins. If they sharpen the immune response to amyloid beta and tau, the collateral damage to nearby healthy brain cells might decrease.

More obviously, these vaccines protect against infections like shingles, which can contribute to neuroinflammation.