Risk Factors for Chickenpox (Varicella)
Between 75 - 90% of chickenpox cases occur in children under 10 years of age. Before the introduction of the chickenpox (varicella) vaccine, about 4 million cases of chickenpox were reported in the U.S. each year. Since a varicella vaccine became available in the U.S. in 1995, the incidence of disease and hospitalizations due to chickenpox has declined by nearly 90%.
Chickenpox usually occurs in late winter and early spring months. It can also be transmitted from direct contact with the open blisters associated with either chickenpox or shingles. (Clothing, bedding, and other such objects do not usually spread the disease.)
A patient with chickenpox can transmit the disease from about 2 days before the appearance of the spots until the end of the blister stage. This period lasts about 5 - 7 days. Once dry scabs form, the disease is unlikely to spread.
Most schools allow children with chickenpox back 10 days after onset. Some require children to stay home until the skin has completely cleared, although this is not necessary to prevent transmission.
Recurrence of Chickenpox. Recurrence of chickenpox is possible, but uncommon. One episode of chickenpox usually means lifelong immunity against a second attack. However, people who have had mild infections may be at greater risk for a breakthrough, and more severe, infection later on particularly if the outbreak occurs in adulthood.
Risk Factors for Shingles (Herpes Zoster)
Shingles affects about one out of every three adults. About 1 million cases of shingles occur each year in the U.S. Anyone who has had chickenpox has risk for shingles later in life. Certain factors increase the risk for such outbreaks.
Review Date: 05/03/2011
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.