Varicella vaccine seems close to licensure in the United States. It is likely to be recommended for routine use in healthy children, either administered singly or as a combination of MMR. Healthy children who have been immunized develop excellent antibody and cell-mediated responses to VZV in the absence of significant adverse effects, and they are well protected against subsequent infection with VZV. Although it will not be known for certain for many years, it seems most unlikely that immunization will result in an increased incidence of zoster, a secondary type of infection with VZV that is caused by reactivation of latent VZV. Varicella vaccine may also be given to healthy adults who have never had chickenpox with a great degree of success, although its protection is somewhat less effective than in children. Leukemic children who are at high risk for developing severe or fatal varicella also derive a great deal of protection from varicella vaccine, but the vaccine must be administered to them with great caution. Other viral vaccines that may be licensed in the future but that are not as fully developed as varicella vaccine include vaccines against CMV, hepatitis A, HSV, and AIDS. These are in various degrees of study, and, should any of them be licensed, it is uncertain whether they would be live attenuated, recombinant, or subunit vaccines. It is hoped, however, that they will eventually be licensed for future use because if effective, they could significantly decrease morbidity and mortality of infants, children, and adults.