Viral strain identification in varicella vaccinees with disseminated rashes

Background. Approximately 15% of recipients of live attenuated varicella va ccine may develop mild breakthrough varicella months to years after immuniz ation. Although some vaccinees will develop tester, it is less common in re cipients of vaccine than in those who have had natural varicella, Objective. To determine the varicella-zoster virus (VZV) strain responsible for breakthrough varicella and tester in recipients of varicella vaccine. Methods. A PCR assay capable of distinguishing wild-type from vaccine strai n VZV was performed on samples from skin lesions from vaccinees with breakt hrough varicella and tester. Results. All of 57 vaccinees with breakthrough varicella, clinically diagno sed on the basis of a generalized maculopapular or vesicular rash, had wild -type VZV infection based on analysis of viral DNA. The Oka vaccine strain of VZV was not identified in any of these cases. In contrast, in 32 patient s with zosteriform rashes, the vaccine strain was identified in 22 samples, and the wildtype strain was identified in 10 samples. Conclusions. Wild-type virus was identified in all generalized rashes occur ring after the immediate B-week postvaccination period. When reactivation o f vaccine strain occurred, it presented as typical tester. We find no evide nce that reactivation of vaccine virus occurs with the clinical picture of generalized rash.