 One dose varicella vaccination introduced in Costa Rica in September 2007 resulted in a 73.8% reduction of reported varicella cases and 85.9% reduction of hospitalizations in the general population, with a 98% decrease in varicella complications among hospitalized patients over an eight-year period. This article was authored by Maria El Avila Aguero, Rolando Uyua Gutierrez, Katia Camacho Badia, and others.