Objective To evaluate the effect of response measures of a varicella outbreak in a district in Shenzhen, and provide evidence for the control of varicella outbreak in the future.
Methods The data of varicella outbreak in a school campus in Shenzhen were analyzed retrospectively, and the control effect was evaluated by using SEIR model of transmission dynamics.
Results The outbreak involved 123 cases of varicella, with an attack rate of 3.40%. In the cases, 92 had history of varicella vaccination. The overall protection rate of varicella vaccine was 55.88%, the protection rate of only one dose of varicella vaccine was 55.20% , and the protection rate of two doses of varicella vaccine was 57.11% , there was a significant difference in attack rate between group of one dose, two doses and unvaccinated group (P<0.001) . There was no significant difference in attack rate between one dose group and two dose group (P>0.05). The SEIR model simulated that the school varicella outbreak duration for 180 days without intervention, 434 cases of varicella would occur, and the case number tend to be zero on day 101. In the fitted conditions of prompt isolation of the first case, isolation of all the cases, and timely emergency vaccination, 10, 92 and 31 cases of varicella would occur, the duration of the outbreak would be 0 day (the case number would be less than 1) , 87 days, and 35 days, respectively. In the fitted condition of four emergency varicella vaccinations in the school, 80 cases would occur, 43 cases less than actual number, and the outbreak would last for 72 days, 2 days less than actual duration, and compared with the situation under 90% vaccination rate, additional 49 cases would occur and the outbreak would last for another 41 days.
Conclusion In the response of varicella outbreak, early detection of the first case, isolation of all the cases and timely emergency vaccination with high coverage are the key measures to control varicella outbreak.
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