Shingles vaccine linked to lower rates of new-onset dementia in Canadian study

Stanford-led researchers analyzed two natural experiments in Canada using a 2016 Ontario shingles vaccine rollout and records for 232,124 older adults, and found an absolute 2.0 percentage-point lower incidence of new dementia diagnoses over 5.5 years among vaccine-eligible groups.

Researchers led by Stanford report natural experiments that suggest shingles (herpes zoster) vaccination averts or delays new-onset dementia. The analysis, published in The Lancet Neurology, focused on a quasi-randomized 2016 vaccine rollout in Ontario and triangulated findings with data from other provinces. The team examined electronic health records and survey-based vaccine coverage for older adults and used quasi-experimental methods to compare eligible and ineligible birth cohorts. The authors note that mechanistic research is needed to understand how targeting herpesviruses might affect dementia risk. Key facts: - The primary analysis estimated the effect of a live attenuated shingles vaccine on new-onset dementia in 232,124 Canadians aged 70 years and older based on an Ontario natural experiment. - Ontario’s 2016 program made residents who turned 71 in or after January 2017 eligible for free vaccination, creating date-of-birth comparison groups (born before Jan 1, 1945; born in 1945; and born Jan 1, 1946–Sept 15, 1951). - Dementia diagnoses were identified from electronic health records covering January 1990 through June 2022, and vaccine coverage was estimated from surveys of older Ontario residents. - Being born immediately before rather than immediately after January 1946 was associated with an absolute 2.0 percentage-point lower likelihood of a new dementia diagnosis over 5.5 years; a January 1945 threshold produced a similar 2.0 percentage-point difference. - The investigators used synthetic difference-in-differences and synthetic control methods to compare dementia trends in eligible Ontario cohorts with ineligible cohorts in other provinces. Summary: The analysis provides evidence consistent with a protective or delaying effect of the live attenuated herpes zoster vaccine on incident dementia in older adults, based on quasi-randomized policy rollouts and complementary methods. The authors call for mechanistic research to clarify how targeting herpesviruses might influence dementia pathophysiology, and note that further evidence could inform discussions about vaccine benefits.