Common vaccines and the risk of dementia: a population‐based study

Abstract Background The growing evidence for an infectious etiology of dementia supports the investigation of immunization as a preventative intervention. Prior observational studies suggesting that common vaccines are associated with an up to 60% decreased risk of dementia had several methodological limitations. Thus, to provide evidence for this question, we assessed in a large population whether common vaccines are associated with a decreased risk of dementia. Method We conducted a population‐based cohort study with a nested case‐control analysis using the Gold and Aurum datasets from the United Kingdom’s Clinical Practice Research Datalink (CPRD). The study cohort included all dementia‐free individuals aged ≥50 years enrolled in the CPRD between January 1988 and December 2018, and followed until March 2021. Each case of dementia identified during follow‐up was matched on sex, age, cohort entry date, duration of follow‐up, and CPRD dataset with up to four controls randomly selected via risk‐set sampling. Conditional logistic regression yielded confounder‐adjusted odds ratios (ORs) with 95% confidence intervals (CIs) of dementia associated with exposure to common vaccines (influenza, pneumonia, shingles, tetanus, diphtheria or pertussis) >2 years before the index date compared to no exposure to these vaccines during the study period. In sensitivity analyses, we applied a longer lag period (10 years) and used active comparators (participation in screening programs for breast and prostate cancer) to account for detection bias. Result Our study cohort included 13,383,431 dementia‐free individuals aged ≥50 years, including 212,562 who developed dementia over a mean 10‐year follow‐up (mean age 70 years; 62% female). Exposure to common vaccines was associated with an increased risk of dementia (OR, 1.38; 95% CI, 1.36‐1.40), compared with no exposure, driven mostly by immunization for influenza (OR, 1.39; 95% CI, 1.37‐1.41). Applying a longer lag period (OR, 1.22; 95% CI, 1.20‐1.24) and using active comparators (versus breast cancer screening: OR, 1.34; 95% CI, 1.26‐1.42 / versus prostate cancer screening: OR, 1.22; 95% CI, 1.14‐1.31) slightly attenuated the risk increase. Conclusion Our large population‐based study showed no decreased risk of dementia associated with exposure to common vaccines. The observed increase in the risk is likely a result of detection bias.