Immunity is generally lifelong. Symptomatic reinfection is rare in healthy persons, although aymptomatic reinfection do occur. Varicella is most common during the late winter and early spring. Aymptomatic primary infection is unusual. Other group of pediatric patients who may experience unusally severe disease or a higher rate of complications include children in the first year of life, adolescents, pregnant adolescents, and patients receiving systemic steroids.
Congenital varicella can also occur if infection of the mother occurs early in pregnancy.
Patients are most contagious for 1 to 2 days before and shortly after the onset of rash. Contagiousness, however, can be as long as 5 days after the onset of lesions, and in immunocompromised patients with progressive varicella, it probably lasts throughout the period of eruption of new lesions. Since the incubation period for varicella is 10 to 21 days, those cases beginning in the first 10 days of life are considered to have been acquired in utero. The prognosis, however, differs markedly between those cases in which maternal illness began 5 or more days from delivery and those in which maternal illness occured 4 days before to 1 day after delivery. In the first group, neonatal disease usually begins with the first 4 days of life, and the prognosis is good.