The Incidence of Zoster after Immunization with Live Attenuated Varicella Vaccine: A Study in Children with Leukemia

Abstract

BACKGROUND: The Oka strain of live attenuated varicella vaccine is immunogenic and highly protective, but there has been concern about the risk of zoster after immunization. METHODS: We examined the incidence of zoster, risk factors for it, and measures of immune response in children with leukemia who received the vaccine and in appropriate controls. RESULTS: After a mean follow-up of 4.1 years, zoster was documented in 13 of the 548 vaccinated children with leukemia (2.4 percent). In a subgroup of 96 vaccinated children matched prospectively with 96 children with leukemia who had had natural varicella infections, there were 4 cases of zoster among the vaccinated children and 15 among the controls, for crude incidence rates of 0.80 and 2.46 cases per 100 person-years, respectively (P = 0.01). Of the total of 13 vaccinated children who had zoster, 11 had a skin rash due to varicella-zoster virus, either from the vaccine itself or from breakthrough varicella after household exposure in the period between immunization and the documentation of zoster. In the 268 children who had any type of rash caused by varicella-zoster virus after vaccination, as compared with those who did not have a rash, the relative risk of subsequent zoster was 5.75. For the 21 vaccinated children who received bone marrow transplants, as compared with those who did not, the relative risk of zoster was 7.5. Cell-mediated immunity as assessed by lymphocyte stimulation was lower in 4 children in whom zoster later developed than in 29 controls who had been vaccinated but who did not have zoster (mean stimulation index, 5.1 vs. 23.8; P = 0.0001). CONCLUSIONS: In children with leukemia who receive the live attenuated varicella vaccine, the subsequent incidence of zoster is lower than in children who have natural varicella infections.