How Vaccines Reduce Dementia Risk

Recent studies have shown convincingly that vaccines against shingles (Herpes zoster) reduce the risk of dementia. The shingles vaccine now in widespread use (Shingrix) has more of an effect than the previous one (Zostavax). A key difference between these vaccines is that Shingrix contains an ‘adjuvant’, an ingredient designed to enhance the vaccine’s effect. It is therefore possible that the adjuvant contributes to Shingrix’ greater effect than Zostavax on reducing dementia.

The new study, supported by the National Institute for Health and Care Research (NIHR) Oxford Health Biomedical Research Centre (OH BRC) supports this possibility. Researchers analysed the health records of over 430,000 people in the USA in the TriNetX network. They found that the Arexvy vaccine - which protects against respiratory syncytial virus (RSV), a common virus that causes cold-like symptoms - was also linked to a significantly lower risk of developing dementia. Arexvy, now offered to adults over 60, contains the same adjuvant as Shingrix. Both vaccines were similarly effective in reducing dementia risk compared to the flu vaccine (which does not contain the adjuvant); in the 18 months following receipt of Arexvy there was a 29% reduction in diagnoses of dementia. These findings held true across a range of additional analyses and were similar in men and women.

It is not clear how the adjuvant, called AS01, might help lower the risk of dementia. However, laboratory studies show that AS01 stimulates cells of the immune system that could help protect the brain from some of the harmful processes underlying dementia. These benefits of the adjuvant in reducing dementia risk could be in addition to the protection that comes from preventing infections like shingles and RSV themselves.

It is not yet known whether these vaccines prevent dementia or, more likely, delay its onset. Either way, the effect is significant, especially given that no other treatments are known that delay or prevent the condition.

The likely beneficial effect on dementia risk is in addition to the vaccines’ proven ability to prevent shingles and RSV, both of which are unpleasant and sometimes serious illnesses.

Lead author, Associate Professor Maxime Taquet, NIHR Academic Clinical Lecturer, Department of Psychiatry, University of Oxford, said: “Our findings show that vaccines against two separate viruses, shingles and RSV, both lead to reductions in dementia. This gives another reason to have the vaccines, in addition to their effectiveness at preventing these serious illnesses.'

Senior author, Professor Paul Harrison, Department of Psychiatry, University of Oxford and Co-Lead for the Molecular Targets theme in OH BRC, said: 'The findings are striking. We need studies to confirm whether the adjuvant present in some vaccines contributes to the reduced dementia risk, and to understand how it does so.'

Reference: Taquet M, Todd JA, Harrison PJ. Lower risk of dementia with AS01-adjuvanted vaccination against shingles and respiratory syncytial virus infections. npj Vaccines. 2025;10(1):130. doi: 10.1038/s41541-025-01172-3

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