Effect of varicella‐zoster virus infection and antiviral treatment on the risk for dementia: A meta‐analysis of observational studies

Background and purpose: There is increasing evidence to support a role for human herpes viruses in the development of neurodegenerative disorders; however, the association between varicella‐zoster virus (VZV) infection and dementia, and the effect of antiviral therapy on the risk for dementia remain unclear. Methods We searched PubMed, Embase, and the Cochrane Library databases from their dates of inception to May 2023. Odds ratios (ORs) with 95% confidence intervals (CIs) served as indicators of effect sizes in evaluations of the effect of VZV infection and antiviral treatment on dementia risk. Subgroup analyses based on study design, study location, diagnostic criteria of dementia, and VZV subtype classification were also performed. Results A total of 10 studies with 316,846 dementia cases were included in the meta‐analysis. We found that any VZV infection (OR: 1.04, 95% CI: .97–1.12; p = .22), herpes zoster (HZ) (OR: 1.05, 95% CI: .96–1.13; p = .28), or HZ involving the cranial nerves (OR: 1.36, 95% CI: .76–2.43; p = .304) was not associated with an increased risk of dementia. The results of subgroup analyses were consistent with these findings. However, patients infected with VZV who received antiviral treatment had a lower OR than untreated patients infected with VZV. Compared to individuals not infected with VZV, antiviral therapy in those infected with VZV was associated with reduced risk for dementia. Conclusion The association between VZV infection and dementia may be masked by antiviral treatment. Further studies with longer follow‐up times that consider the severity of VZV infection and antiviral treatment are needed to clarify the contribution of VZV infection to the risk for dementia. This systematic review and meta‐analysis provide evidence of the effect of VZV infection and antiviral treatment on the risk for dementia. The findings suggest that the association between VZV infection and dementia may be masked by antiviral treatment. Further studies that take antiviral treatment into consideration are needed to establish this actual association.