Abstract: ObjectiveTo analyze the effectiveness of varicella vaccine in varicella outbreaks, so as to provide scientific basis for varicella control and the adjustment of immunization strategy. MethodsFour schools in Guangdong Province which experienced varicella outbreaks were selected as study fields. Students who had not previously had varicella were selected from classes with high morbidity of varicella as study subjects. Data on inoculation history of varicella vaccine and varicella occurrence were collected from the subjects. Retrospective cohort study was used to analyze the relationship between the inoculation history of varicella vaccine and attack rates of varicella during the outbreak, and the effectiveness of varicella vaccine was then calculated. ResultsAmong the subjects attack rates of varicella were 28.3% (53/187), 32.9% (24/73), 31.9% (37/116), and 36.4% (36/99), respectively, in four schools with outbreaks of varicella. The inoculation rates of varicella vaccine were 27.3% (51/187), 78.1% (57/73), 87.1% (101/116), and 49.5% (49/95), respectively. Among the subjects vaccinated with 1 dose of varicella vaccine in the four schools, the relative risks developing varicella were 0.52, 0.69, 0.50, and 0.39, respectively; the effectiveness of varicella vaccine was 48%, 31%, 50%, and 61% for students vaccinated with 1 dose of varicella vaccine, but 100% for those vaccinated with 2 doses.ConclusionIn the population with high exposure to varicella, one dose of vaccine is not enough for varicella prevention. Inoculation schedule of varicella vaccine should be adjusted from one dose to two doses among students to reduce the varicella outbreaks effectively.