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.