Scientists behind a study suggesting GSK's respiratory syncytial virus (RSV) vaccine could be protective against dementia have said the adjuvant used in the shot may be responsible.
The new observational study, carried out by the University of Oxford and funded by the UK government, found a 29% reduction in the risk of dementia in the 18 months after receiving the Arexvy jab, and follows another study by the team – reported last year – that found a 17% drop with GSK's shingles vaccine Shingrix.
Now, the scientists – led by Professors Maxime Taquet and Paul Harrison – are speculating that the common thread between the two studies is the AS01 adjuvant used in both Arexvy and Shingrix to boost immune responses to the shots. And that could explain why GSK's older shingles vaccine Zostavax – which is not adjuvanted – had a reduced effect.
The latest analysis, published in the Nature journal npj vaccines, draws on information from electronic health records for more than 430,000 people in the US in the TriNetx network. It showed that both Arexvy and Shingrix were similarly effective in reducing dementia risk compared to flu vaccines, which do not contain the AS01 adjuvant.
It is not clear how AS01 might help lower the risk of dementia, but Oxford University said lab studies show that the adjuvant stimulates cells of the immune system that could help protect the brain from some of the harmful processes underlying dementia.
Adding Arexvy into its calculations helped the team explore one other possibility; namely, that targeting the herpes zoster virus that causes shingles could be protective in some way.
"It is not yet known whether these vaccines prevent dementia or, more likely, delay its onset," according to a statement from the university. "Either way, the effect is significant, especially given that no other treatments are known that delay or prevent the condition."
An effect on dementia, while still speculative, builds to the case for use of the RSV and shingles vaccines in older adults, given that both infectious diseases can be debilitating and potentially serious.
"Dementia is not an inevitable part of ageing. Identifying ways to reduce dementia risk is a priority for research, and vaccination offers an intriguing area of exploration," commented Dr Julia Dudley, head of research at Alzheimer's Research UK.
While the study attempted to adjust for factors that could influence risk, such as underlying health conditions and some lifestyle and environmental factors, it cannot rule out that the link between vaccine and dementia risk is due to other factors, she pointed out – something that is acknowledged in the journal paper.
"We do not know if the adjuvant is reducing the risk of dementia or delaying its onset. The follow-up period was only 18 months, so more research is needed to determine the potential long-term effects of the vaccines," added Dudley.
"As we understand more about the biological mechanisms behind any protective effects seen with vaccines, we may be able to investigate new treatment approaches."
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