Chicken pox is caused by varicella zoster virus. In immunocompetent children, varicella is usually not a serious disease, but can cause severe morbidity and mortality in adults and in immunocompromised individuals. Administration of varicella vaccine within the first few days after exposure will produce a protective immune response in VZV seronegative individuals. About half of patients receiving post-exposure immunization may still develop some signs and symptoms of chickenpox, but the disease manifestations are usually very mild. Postexposure vaccination appears to be more effective and less expensive. This approach may be useful for managing VZV exposures that occur in a family. The virus is resistant to the powerful antiviral drug acyclovir.The possible choice of drug is foscarnet.