Association of Influenza Vaccination and Dementia Risk: A Meta-Analysis of Cohort Studies.

BACKGROUND

Dementia is a critical global public health problem. Previous cohort studies have found that influenza vaccination can decrease the risk of dementia.

OBJECTIVE

This meta-analysis aimed to systematically examine the relationship between influenza vaccination and dementia risk.

METHODS

We searched PubMed, Embase, Web of Science, ScienceDirect, medRxiv, and bioRxiv for studies investigating dementia risk based on influenza vaccination status, up to September 14, 2022. Relative risks (RRs) and 95% confidence intervals (95% CIs) were pooled in the meta-analysis. Subgroup analyses and sensitivity analyses were conducted as well.

RESULTS

Of the 4,087 articles initially reviewed, 6 cohort studies were included in the final meta-analysis, and all eligible studies were at low risk of bias. There were 2,087,195 participants without dementia at baseline (mean age: 61.8-75.5 years, 57.05% males), and 149,804 (7.18%) cases of dementia occurred during 4.00-13.00 years of follow-up. Pooled analysis of adjusted RRs found that influenza vaccination could reduce dementia risk by 31% (RR = 0.69, 95% CI: 0.57-0.83). Subgroup analyses showed that in the study with a mean age of 75-80 years or 75%-100% males, the association was generally weakened compared with studies with a mean age of 60-75 years or 25%-50% males. The results were stable in the sensitivity analyses, and no publication bias was observed.

CONCLUSION

Influenza vaccination in older adults was markedly associated with a decreased risk of dementia. More mechanistic studies and epidemiological studies are needed to clarify the association between influenza vaccination and decreased dementia risk.