This summary discusses varicella in neonates. Varicella in adults and children is addressed separately.

Neonatal varicella, or neonatal chickenpox, is infection with varicella-zoster virus (VZV) during the first 4-6 weeks of life. Neonates may be infected (1) in utero by transplacental viremia, (2) at birth by ascending infection, or (3) after birth by respiratory droplets or direct contact with infectious lesions. The incubation period of VZV is usually between 10 and 14 days; therefore, onset of symptoms within the first 10 days of life is usually caused by intrauterine transmission. Onset of symptoms after 10 days is usually indicative of postnatally acquired infection.

Intrauterine-acquired neonatal varicella is common in infants born to mothers who contract a primary varicella infection during the last 3 weeks of pregnancy. The severity of neonatal disease is dependent on the presence of transplacentally acquired maternal antibodies. Hence, onset of the rash of primary maternal VZV infection between 6 and 21 days prior to delivery allows for maternal antibody production, transplacental transfer to the fetus, and nonfatal neonatal varicella. Conversely, onset of maternal rash between 5 days before and 2 days after delivery does not allow sufficient time for maternal antibody production, and one can expect a fulminant course.

Postnatally acquired VZV infections are usually self-limited in healthy full-term infants. However, severe varicella may result in neonates less than 28 weeks' gestation or below 1000 grams at birth.