Herpes zoster in the context of varicella vaccination - An equation with several variables.

Background: Varicella and herpes zoster (HZ), diseases both caused by the varicella zoster virus (VZV), are vaccine-preventable. However, the hypothesis that childhood varicella vaccination may increase the incidence of HZ hinders varicella universal routine vaccination (URV) implementation in many countries.

Methods: This non-systematic and narrative review of the literature considers the burden of varicella and HZ, and the effectiveness of the respective vaccines. We present the factors involved in the interplay between varicella vaccination and HZ incidence, including the roles of exogenous and endogenous boosting. We review HZ incidence model predictions, and compare these with real-world evidence, which has accumulated since varicella URV was introduced.

Conclusion: Although more research and longer surveillance are needed, available real-world evidence has not confirmed the model-predicted increase in HZ incidence, associated with childhood varicella URV. Although there is a rising incidence of HZ globally, this trend appears to be predominantly the result of an aging population. Vaccination against varicella in childhood provides significant benefits with respect to the medical, societal and economic burdens of the disease. Therefore, a theoretical concern of an increased burden of HZ with varicella vaccination programs should not prevent children from being protected against the disease.