The Food and Drug Administration licensed a live-virus varicella vaccine (Varivax; Merck & Co Inc, West Point, PA) in March 1995. Prelicensure adverse events were minimal; however, since licensure and increased vaccine use, rare previously undetected risks have arisen. Presented here is the clinical course of a previously undiagnosed, human immunodeficiency virus-infected boy who developed dissemination of the vaccine strain of varicella zoster after immunization. chickenpox, human immunodeficiency virus, pneumonia, encephalopathy, varicella vaccine, adverse events, dissemination.

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