Varicella, commonly known as chickenpox, is a disease characterized by skin lesions and low-grade fever, and is common in the United States and other countries located in areas with temperate climates. The incidence of varicella is extremely high; almost everyone living in the United States is exposed to the disease, usually during childhood, but sometimes in adulthood. In the United States, about 3.9 million people a year contract varicella. A highly contagious disease, varicella is caused by Varicella-Zoster virus (VZV), the same virus that causes the skin disease shingles. For most cases of varicella, no treatment besides comfort measures and management of itching and fever is necessary. In some cases, however, varicella may evolve into more serious conditions, such as bacterial infection of the skin lesions or pneumonia. These complications tend to occur in persons with weakened immune systems, such as children receiving chemotherapy for cancer, or people with...