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The human α-herpesvirus, varicella-zoster virus (VZV), is a highly successful pathogen that has coevolved with its human hosts over millennia. The majority of the world’s population has experienced primary VZV infection as varicella (“chickenpox”), with the acquisition of both lifelong immunity against reinfection and the risk of viral reactivation as zoster (“shingles”). In most children, chickenpox is a mild illness in which viral replication rapidly subsides. However, severe and complicated varicella does occur in previously healthy children and at much higher rates in certain risk groups (eg, immunocompromised persons, adults, newborns). The medical importance of VZV also extends to reactivation disease, which poses a major societal burden of morbidity in the form of postherpetic neuralgia, particularly in elderly individuals. A successful vaccination program against varicella is having profound effects on the epidemiology of VZV in the United States.


Varicella is acquired through close contact with an infected individual. Natural varicella is the most communicable form of varicella-zoster virus (VZV) disease: household attack rates approach 90%, and outbreaks occur readily within groups of susceptible children.1 A milder form of varicella, occurring in vaccinated individuals with partial immunity, is only one third as transmissible,2 whereas zoster represents the least contagious form of disease.

In unvaccinated populations in temperate climates, seasonal peaks of varicella occur in the spring. These epidemics occur on a background of endemic disease, and 84% of children acquire infection by age 15 years.3,4 In contrast, the incidence of varicella in the tropics does not vary by season and tends to be delayed until adolescence or adult life.3 At this age, morbidity and mortality from varicella are significantly greater than in childhood, for reasons that are poorly understood.

Aside from adult age, the greatest risks for severe/fatal varicella are cellular immunocompromise (congenital or acquired), infancy (particularly, the neonatal period), and pregnancy (Table 314-1). In the prevaccine era, varicella was associated with approximately 11,000 hospitalizations and in excess of 100 deaths annually in the United States.5,6 Much of this burden was borne by previously healthy children. The epidemiology of VZV has been transformed since the introduction of universal varicella vaccination in the mid-1990s. The incidence of varicella has been strikingly reduced across all age groups, with concomitant reductions in office visits, hospitalizations, and deaths from varicella.7-10

Table 314-1. Patients at High Risk to Develop Severe Varicella Zoster Virus Infections and Guidence to Therapy

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