Symposium on infectious complications of neoplastic disease (Part II). Immunoprophylaxis of varicella-zoster infections.

Because it is possible to identify groups of persons with a high risk of varicella development and also because it is possible to anticipate when an attack may occur, immunoprophylaxis for varicella has met with great success. In contrast, the nature of zoster--its unpredictability and low attack rate--makes immunoprophylaxis much more difficult to implement. Varicella may be modified by administration of varicella-zoster immune globulin within three days of a known exposure to the virus. Although interferon has not yet been used in an attempt to prevent or modify varicella in humans, it has been used successfully to abort an outbreak of simian varicella in a monkey colony. Thus it might be clinically useful, particularly for those who cannot be given varicella-zoster immune globulin within three days of exposure. Transfer factor has also been shown to induce at least partial immunity to varicella in children with leukemia. The duration of this protection is unknown, and further study of the efficacy of transfer factor against both varicella and possibly even against zoster seems warranted. Live attenuated varicella vaccine, although still experimental, seems now to be the most practical way to prevent severe varicella in high-risk persons. The vaccine is safe and immunogenic, even in children with underlying leukemia who are still receiving chemotherapy. Studies in Japan, Europe, and the United States have shown that most vaccinated leukemic children who are exposed are protected against severe disease, although mild breakthrough cases have been reported. Varicella vaccine's potential to cause zoster remains under study.