Cost-benefit analysis of universal varicella vaccination in the U.S. taking into account the closely related herpes-zoster epidemiology.

Many models concur that universal varicella vaccination of children is beneficial from the perspective of reducing societal costs. Yet, the majority of such cost analyses have been modeled under the assumption that varicella vaccination has no adverse effect on the closely related herpes-zoster (HZ) epidemiology. Historical models have assumed that asymptomatic endogenous reactivation is the chief mechanism of boosting that suppresses the reactivation of HZ and that immunity wanes due to the aging process. Recent studies suggest instead that periodic exogenous exposures to wild-type varicella are the predominant factor influencing the curve of increasing HZ incidence rate with advancing age among individuals <50, after which an age-related decline dominates in the elderly. Based on a realistic age-structured model, we compare differences in outcomes of the number of HZ cases and direct medical costs associated with the population existing in 2000 and as it ages (according to the mortality given in the 2000 U.S. census) during the following 50 years with and without implementation of universal varicella vaccination. Under universal varicella vaccination, we assume that 15 years post-licensure, the boosting mechanism known as asymptomatic endogenous reactivation principally serves to limit HZ incidence to 550 per 100,000 person-years in unvaccinated individuals <50 with a previous history of natural varicella--since there has been a vaccine-induced decline in exogenous boosting. We estimate universal varicella vaccination has the impact of an additional 14.6 million (42%) HZ cases among adults aged <50 years during a 50 year time span at a substantial cost burden of 4.1 billion US dollars or 80 million US dollars annually utilizing an estimated mean healthcare provider cost of 280 US dollars per HZ case.