To analyze the epidemiological characteristics of a varicella outbreak in X Primary School in 2024, evaluate the protective efficacy of varicella vaccine, summarize the characteristics of varicella outbreaks, and provide references for the prevention and control of infectious diseases in schools and emergency response. Methods: Symptoms of all ill students were analyzed to clarify the epidemiological characteristics, and the Cox regression model was used to analyze the protective efficacy of varicella vaccine. Results: The varicella epidemic lasted for one month, involving 3 classes in 2 grades. A total of 16 varicella cases were identified in the school, with an attack rate of 1.78%. The vaccination status of 142 students was analyzed for vaccine protective efficacy. Comparison with unvaccinated students showed that the protective efficacy of 1 dose of varicella vaccine was not significant, while the protective efficacy of 2 doses of varicella vaccine was 82.10%. Conclusion: Vaccination with 2 doses of varicella vaccine provides the best protective effect. Timely isolation of ill students after the outbreak can effectively control large-scale varicella outbreaks.