A Canadian study from a network of primary care records found that vaccination against herpes zoster (shingles) is associated with a significantly lower risk of dementia. A claim for free live attenuated vaccine Zostavax has been associated with this effect. Other studies, including a Welsh analysis of medical records of more than 280,000 seniors, found a 20% lower relative risk of dementia over 7 years after vaccination. In the US, retrospective analyzes in patients over 65 years showed a 31 to 35% reduction in the risk of dementia after adjusting for risk factors. A meta-analysis of five studies with more than 103,000 vaccinated individuals estimated an overall risk of OR ≈ 0.84. A cohort study with 436,788 people confirmed a similar effect with the AS01-adjuvanted Shingrix vaccine, with no difference compared to other vaccines with this adjuvant.