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Some vaccines may reduce the risk of dementia through a double effect in which the jabs help protect the brain through their added “adjuvant” chemicals as well as by suppressing viruses, according to a study by Oxford university.
The analysis of health records of 430,000 people in the US, published on Wednesday, found that vaccination against respiratory syncytial virus (RSV) with GlaxoSmithKline’s Arexvy was associated with a 29 per cent decrease in diagnoses of Alzheimer’s and other forms of dementia during the following 18 months.
The findings add to growing evidence of a link between viral infections and dementia, but the Oxford scientists were most excited about their conclusion that a significant part of the dementia reduction might be due to the AS01 adjuvant — a mixture of fatty molecules that are added to enhance the vaccine’s effectiveness by priming the recipient’s immune system.
That could open the way for a new approach to dementia prevention, said Paul Harrison, Oxford professor of psychiatry. “The findings are striking,” he said. “We need more studies to confirm whether the adjuvant . . . contributes to the reduced dementia risk, and to understand how it does so.”
Previous studies showed that Shingrix, GSK’s most recent vaccine against shingles — which is caused by the Herpes zoster virus — cut the risk of dementia by 27 per cent. Shingrix contains the same AS01 adjuvant, unlike its predecessor Zostavax, which showed a much smaller reduction.
Shingrix and Arexvy decreased dementia by similar proportions, though they target very different viruses, contributing to the Oxford team’s argument that the adjuvant played an important role.
Another boost to their argument “is the fact that a protective effect is seen within a few months of vaccination, as it seems unlikely that enough infections would be prevented during such a short timeframe to explain the magnitude of the protection”, Harrison said.
How long the protection lasts is unknown.
The scientists are not sure how AS01 might lower the risk of dementia, though the effect is likely to involve the immune system in the brain, which has been shown in recent research to play an important role in Alzheimer’s disease.
The study, published in the journal npj Vaccines, compared the health of people in the TriNetX data network who had received Shingrix and Arexvy, singly or in combination, with a control group that only received a flu vaccine.
“One of the strengths of the study is that it adjusted for factors that could influence risk, such as underlying health conditions and some lifestyle and environmental factors,” said Julia Dudley, head of research at the charity Alzheimer’s Research UK.
“But we cannot rule out that the link between vaccine and dementia risk is due to other factors not captured in this study . . . As we understand more about the biological mechanisms behind any protective effects seen with vaccines, we may be able to investigate new treatment approaches.”
To maintain independence, the researchers excluded GSK from any involvement in the analysis. The company said: “This is an interesting independent study. We are collaborating with UK Dementia Research Institute and Health Data Research UK to investigate the potential links between shingles vaccination and reduced dementia risk. We look forward to assessing these new findings.”
