Chicken pox is now believed to be the cause of one third of stroke cases in children.[2] The most common late complication of chicken pox is shingles, caused by reactivation of the varicella zoster virus decades after the initial episode of chickenpox.

# Women who get chickenpox during pregnancy are at risk for congenital infection of the fetus.
# Newborns are at risk for severe infection, if they are exposed and their mothers are not immune.
# A secondary infection of the blisters may occur.
# Encephalitis is a serious, but rare complication.
# Reye's syndrome, pneumonia, myocarditis, and transient arthritis are other possible complications of chickenpox.
# Cerebellar ataxia may appear during the recovery phase or later. This is characterized by a very unsteady walk.

About 1 of every 100 children infected with chickenpox will develop a severe lung infection (pneumonia), an infection of the brain (encephalitis), or a problem with the liver. Dangerous skin infections also can occur. Before the introduction of the vaccine, about 100,000 people were hospitalized and 100 people in the United States died each year of chickenpox, most of them previously healthy children. Adolescents and adults who develop chickenpox are also at high risk of developing serious complications.