This summary discusses varicella in children. Neonatal varicella is addressed separately.

Varicella, or chickenpox, is an acute, highly contagious exanthem caused by primary infection with varicella-zoster virus (VZV). The virus is believed to be spread by respiratory droplets and skin vesicles from individuals with varicella or herpes zoster (a dermatomal rash caused by reactivated endogenous VZV) to the respiratory tract of susceptible children. In immunologically normal children, the illness typically begins after an incubation period of 2-3 weeks, lasts 3-7 days, and resolves without complication. One varicella episode usually confers lifelong immunity, although reinfections have been documented.

In rare cases, varicella is associated with prolonged courses and severe complications, including bacterial superinfection, pneumonia, encephalitis, bleeding disorders, and hepatitis. Adolescents and immunocompromised children (eg, malignancy, congenital defects in cell-mediated immunity, organ transplant recipients, children receiving long-term immunosuppressive therapy, or human immunodeficiency virus [HIV]-infected children) are at elevated risk for complications.

Varicella was a common viral disease of children until childhood vaccination in the United States became routine during the 1990s. The disease remains common in nondeveloped countries and is seen more frequently in older children and adults.

In vaccinated individuals, "breakthrough varicella" can occur. Illness is usually mild (low fever or no fever, fewer lesions [less than 50], less pruritic, shorter duration, absence of vesicles), although some patients present similar to unvaccinated individuals.

Note: In 2022 and 2023, pediatric invasive group A streptococcal (iGAS) infections and noninvasive group A streptococcal infection cases have been associated with respiratory infections due to parainfluenza, rhinovirus, enterovirus, influenza, and human metapneumovirus, among other viruses. Concurrent or preceding viral infections, including varicella (chickenpox), may increase risk for iGAS infection. Severe outcomes of iGAS infections include necrotizing fasciitis, streptococcal toxic shock syndrome, and death.

Related topic: varicella pneumonia