Older US adults who receive the AS01-adjuvanted shingles or respiratory syncytial virus (RSV) vaccines may be at lower risk for dementia in the next 18 months, University of Oxford researchers write in npj Vaccines.
Because no difference was observed between the two vaccines, both of which contain the AS01 adjuvant to boost immune response, the authors suggest that AS01 itself may contribute to the lower dementia risk.
The team analyzed electronic health record (EHR) data to determine whether AS01 has a role in reducing the risk of dementia seen with the AS01-adjuvanted shingles vaccine Shingrix by comparing it with the AS01 RSV vaccine Arexvy and with the flu vaccine.
Shingrix has been linked to a lower risk of dementia than the live vaccine, Zostavax, which was discontinued in the United States because Shingrix is more effective against infection in both men and women, the study authors noted.
“There is growing evidence that vaccination against shingles (also known as herpes zoster, which is caused by reactivation of the varicella-zoster virus) protects against dementia, with some studies showing a stronger effect in females,” they wrote.
Men, women both benefit
In total, 35,938 participants received the AS01 RSV vaccine only (average age, 72.8 years), 103,798 were given only the AS01 shingles vaccine (69.2 years), and 78,658 received both (72.4 years). They were matched to flu vaccine recipients and those who received neither the shingles nor the RSV vaccine.
These correspond to 29%, 18%, and 37% additional time spent diagnosis-free, or 87, 53 and 113 days for those diagnosed within 18 months of vaccination, respectively.
Compared with flu vaccine recipients, those given the RSV or shingles vaccine had 18% to 37% lower odds of receiving a dementia diagnosis in the next 18 months (ratio of restricted mean time lost was 0.71 for RSV only, 0.82 for shingles only, and 0.63 for both vaccine).
“These correspond to 29%, 18%, and 37% additional time spent diagnosis-free, or 87, 53 and 113 days for those diagnosed within 18 months of vaccination, respectively,” the authors wrote.
The difference in the risk of dementia wasn’t significantly different between those who received either the shingles or RSV vaccine and those given both. Results were similar in both men and women and when including participants diagnosed as having dementia in the first 3 months of follow-up.
“Results were similar for the composite outcome of dementia or death,” the researchers wrote. “Results in terms of dementia subcategories had wide CIs [confidence intervals], reflecting the low incidence of some subcategories and the lack of use of subcodes in routine clinical practice, except for ‘Unspecified dementia’ that mirrored the primary finding.”
AS01 may play a role
The mechanisms behind the anti-dementia effects of both AS01 vaccines could include the prevention of shingles or RSV infection, but the authors noted that this is unlikely because the effects were seen in a very short timeframe.
These findings justify further clinical and mechanistic studies to confirm and understand the protective effects and their duration.
“In addition, if the adjuvanted vaccines exerted their protective effect via separate mechanisms, we would expect an additive protective effect in individuals who received both vaccines compared to those who received only one—a pattern not observed here,” they wrote.
The study results, they said, suggest that the AS01 shingles and RSV vaccines provide some protection against dementia.
“Our data provide support for the hypothesis that, besides protection against their target infection, these vaccines could well protect against dementia via the action of the AS01 components through specific immunological pathways,” they concluded. “These findings justify further clinical and mechanistic studies to confirm and understand the protective effects and their duration.”
