BACKGROUND

Observational studies suggesting that immunizations strongly decrease the risk of dementia had several methodological limitations. We assessed whether common vaccines are associated with the risk of dementia.

METHODS

We assembled a population-based cohort of dementia-free individuals aged ≥50 years in the United Kingdom's Clinical Practice Research Datalink between 1988 and 2018. Using a nested case-control approach, we matched each patient with dementia with 4 controls. Conditional logistic regression yielded confounder-adjusted odds ratios (ORs) with 95% confidence intervals (CIs) of dementia associated with common vaccines >2 years before the index date compared with no exposure during the study period. Moreover, we applied a 10-year lag period and used active comparators (participation in breast or prostate cancer screening) to account for detection bias.

RESULTS

Common vaccines were associated with an increased risk of dementia (OR, 1.38 [95% CI, 1.36-1.40]), compared with no exposure. Applying a 10-year lag period (OR, 1.20 [95% CI, 1.18-1.23]) and comparing versus prostate cancer screening (1.19 [ 1.11-1.27]) but not breast cancer screening (1.37 [1.30-1.45]) attenuated the risk increase.

CONCLUSIONS

Common vaccines were not associated with a decreased risk of dementia. Unmeasured confounding and detection bias likely accounted for the observed increased risk.