Prospects for use of a varicella vaccine in adults.

Five to 10% of people reach adulthood still susceptible to VZV, which generally causes more severe primary disease in adults than seen in children. A live attenuated varicella vaccine was developed in Japan in the early 1970s and has now been tested in several trials in healthy children, immunocompromised children, and healthy adults. The vaccine is highly immunogenic in healthy children, conferring immunity for at least 7 to 10 years with a high degree of protective efficacy. In several trial in adults, the vaccine has been shown to be highly immunogenic. Humoral and cell-mediated immunity wanes in vaccinated adults, however, with antibodies to VZV detectable in approximately only 80% of vaccinated individuals after 1 year, and in approximately 70% from 2 to 6 years after vaccination. In leukemic children who have been vaccinated, however, this loss of detectable antibody has not been correlated with a reduction in protection during this time. Similar analyses have not been made in vaccinated adults because the numbers intimately exposed to VZV have been small. Protective efficacy after household exposure is approximately 65% in adults; however, when breakthrough (i.e., in those who have seroconverted) illness has occurred, it has invariably been mild, so that efficacy in preventing severe disease has been 100%. "Vaccine failures," however, may develop full-blown varicella. Side effects of immunization in adults are mild: a transient local reaction occurs in 10 to 21% and a mild rash in 6 to 8%. There is a theoretical risk of transmission of the attenuated virus if a vaccine-induced rash occurs, which has been documented only in contacts of vaccinated leukemics (any secondary disease has also been mild). To date, there has been no evidence that vaccination increases the risk of developing zoster; on the contrary, studies in leukemic children, who may be considered a "sentinel population" in this regard, suggest that the risk of zoster after vaccination may be reduced compared with the risk after natural infection. Susceptible adults who would most benefit from vaccination against VZV include health care workers, those who care for small children, women of child-bearing age prior to pregnancy, military recruits, and college students.