The live, attenuated varicella vaccine was licensed in early 1995 and its use has been recommended by the Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention. Black and associates report data on safety and efficacy compiled by the Northern California Kaiser Permanente Medical Care Program, which instituted varicella vaccination into its preventive care program in April 1995.
From April 1, 1995, to December 31, 1996, a total of 89,753 members received at least one dose of varicella vaccine; 3,625 recipients of the vaccine were 13 years of age or older. During the study period, only two deaths occurred in this group within 60 days of vaccination. One death occurred in an 87-year-old man who died of prostate cancer 34 days after vaccination, and the second death occurred in a healthy 16-month-old child who drowned 13 days after vaccination. Neither of the deaths was thought to be caused by varicella vaccination.
No cases of cerebellar ataxia or encephalopathy were identified after vaccination. The risk of seizures did not increase following varicella vaccination when the results were adjusted for concomitant administration of other vaccines. The vaccine was not associated with the occurrence of anaphylaxis or hives. An increased risk of mild gastroenteritis was noted after receipt of the varicella vaccine.
During the first 28 months of the study, 335 cases of varicella-like rash occurred, for a breakthrough rate of 2.5 percent per year. Of these cases, eight were classified as severe (> 300 lesions). Twenty-three cases of zoster were reported by parents during telephone interviews. Of these cases, 10 were evaluated by physicians, and two were considered compatible with zoster, giving a herpes zoster rate of 1.5 cases per 10,000 person-years of follow-up.
The authors conclude that the varicella vaccine appears to be safe and free of serious side effects. The rates of varicella-like rash and of breakthrough varicella are low and consistent with the rates observed in prelicensure studies. Long-term effectiveness studies are ongoing.
editor's note: The American Academy of Family Physicians recommends varicella vaccination at any visit on or after the first birthday in unimmunized children who do not have a reliable history of chickenpox. Susceptible persons 13 years of age or older should receive two doses, given at least four weeks apart. The rate of complete protection as a result of the varicella vaccine is about 90 percent. This vaccine can be given to immunocompromised children, including children with leukemia, and to bone marrow transplant recipients when immune function recovers. Inactivated varicella vaccine can reduce mortality related to varicella zoster virus reactivation in high-risk populations. The duration of immunity is unknown, but studies indicate persistent immunity for up to 10 years after vaccination. Small studies in Japan suggest that immunity persists for as long as 20 years.—r.s.