Strategies to prevent varicella among newly arrived adult immigrants and refugees: a cost-effectiveness analysis.

In temperate, industrialized countries, such as Canada, varicella is a common disease in childhood [1]. In tropical countries, for reasons that are not entirely clear, varicella occurs among young adults. Seroprevalence data from tropical regions suggest that up to 30% of individuals are susceptible to varicella at 20 years of age, and 5%–10% remain susceptible at 30 years of age [2, 3]. There have been many reported outbreaks of varicella in immigrant populations in industrialized countries, suggesting that foreign-born adults are disproportionately susceptible [4–6]. Recent immigrants also have a high risk of exposure, because many are the parents of young children, who have a high annual incidence of varicella unless they are vaccinated. Varicella is more severe in adults than in children and is associated with a greater risk of complications and death [7]. The fetuses and neonates of pregnant women who develop varicella may develop congenital or neonatal varicella, with high case-fatality rates [8, 9]. Preventing varicella in young adult immigrants, therefore, is important because of the susceptibility of this population and the potential for adverse outcomes. A live-attenuated vaccine was licensed in Canada in 1998 and is now universally available for children !13