In a population-based cohort study, receipt of common vaccines (particularly for influenza and pneumococcus) was associated with increased risk for subsequent dementia.

Infectious diseases have been speculated to be linked to development of dementia. Furthermore, observational studies have suggested that several routine immunisations are associated with decreased risk for dementia, leading to the proposal that vaccination could serve as a preventive measure against this condition. To examine this further, researchers used the UK Clinical Practice Research Datalink in a large, population-based cohort study to assess whether receipt of common vaccinations (influenza, pneumococcus, shingles, tetanus, diphtheria and pertussis) is associated with decreased risk for developing dementia after a two-year lag period. The study sample included 13,383,431 dementia-free individuals aged 50 years or older who were enrolled between January 1988 and December 2018. Those who received vaccines were noted to be, on average, sicker than unvaccinated cases and controls.

Contrary to their expectations, the authors found that, compared with no exposure, vaccination was associated with increased risk for dementia (odds ratio, 1.38; 95% CI, 1.36–1.40), most of which was associated with influenza and pneumococcal immunisation. In addition, dementia risk rose with an increasing number of administered vaccines, with the greatest increase immediately after the end of the two-year lag.

Comment: As the authors note, these data do not support a role for vaccination to prevent dementia. Moreover, the observed increase in risk with vaccination was unexpected – and not clearly biologically plausible. As the authors and editorialists point out, unmeasured and confounding detection biases probably account for these results; for example, people with dementia may be more likely to be vaccinated due to caregivers’ concerns or because of residence in skilled nursing facilities. The findings in this study are not the last word on the issue.

At the time we reviewed this paper, its publisher noted that it was not in final form and that subsequent changes might be made.

Neil M. Ampel

Douros A, et al. Common vaccines and the risk of incident dementia: a population-based cohort study. J Infect Dis 2022 Dec 21; e-pub (https://doi.org/10.1093/infdis/jiac484).

Salmon DA, et al. Commentary on ‘Common vaccines and the risk of dementia: a population-based cohort study’: science can be messy but eventually leads to truths. J Infect Dis 2022 Dec 21; e-pub (https://doi.org/10.1093/infdis/jiac487).