The dementia protection hiding in plain sight

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Vaccination during adulthood is associated with significantly reduced risks of dementia. The evidence is as powerful as it is surprising.

A large study found that adults aged 65 and over who had received the adult tetanus, diphtheria and pertussis (whooping cough) vaccine had a 42 per cent lower risk of developing dementia during follow-up. Pneumococcal vaccination is associated with nearly a 30 per cent reduction in dementia incidence. Evidence from nearly 300,000 older people who started off dementia-free showed a 30 per cent reduction in the risk of dementia over the next ten years if they'd had the influenza vaccine. A review of over 100,000 people found around a 24 per cent reduction in dementia incidence in those immunised against shingles (Varicella zoster).

It's hard to find another intervention that's associated with such powerful effects, and the evidence suggests that the benefit starts from about the age of 50.

It's hard to find another intervention that's associated with such powerful effects, and the evidence suggests that the benefit starts from about the age of 50. It could be earlier. All of the above findings allow for other factors that could explain the effect, such as differences between people who are more or less likely to be vaccinated in the first place.

The question is why?

Varicella zoster virus is a herpes virus, and researchers have long wondered whether herpes infections are a trigger for cognitive decline leading to dementia, given their affinity for the nervous system. At least one of the ways the zoster vaccine works to prevent dementia appears to be by keeping the virus at bay.

But there also seems to be a separate effect on the immune system, and this may help explain why influenza, pneumococcal, and tetanus/whooping cough vaccines appear to have a preventive effect as well. The leading theory is that chronic low-grade inflammation, driven in part by persistent viral activity, is a key pathway in dementia development. Vaccination may reduce that inflammatory burden over time, offering protection that goes well beyond the infections they were designed to prevent.

COVID-19 is relevant here too. A meta-analysis of over 800,000 people found that 65 per cent of those aged 65 and over who were hospitalised with COVID-19 developed new symptoms of cognitive impairment. A UK Biobank study comparing people aged over 50 who had COVID with those who had not found a 58 per cent increased risk of all-cause new onset dementia, particularly vascular dementia. COVID-19 vaccination reduces the risk of Long COVID significantly, and while direct evidence on cognitive outcomes is still emerging, the overall picture strongly favours vaccination.

With flu season underway, it is worth having these conversations proactively, particularly with adults over 50 who may be behind on pneumococcal, shingles, or Tdap vaccines. The dementia prevention angle gives the conversation a new dimension that many people have not yet considered.