Comparison of varicella outbreaks in schools in China during different vaccination periods

The purpose of this study was to investigate the outbreak trend of chickenpox and the epidemiological characteristics of outbreak related cases from 2017 to 2021, and compare the impact of voluntary self-funded single dose vaccination versus mandatory two-dose vaccine vaccination on varicella outbreaks. The data of varicella outbreaks in Jiangsu Province from 2017 to 2021 come from the national public health emergency management information system. We randomly chose 70 outbreaks from 2019 to 2020 for study in order to better understand the features and regularity of breakthrough varicella(BV). In pilot cities with two doses of free VarV, the number of outbreaks decreased from 306 in 2017 to 123 in 2021, while the total number of cases related to the outbreak decreased by 64.6% (P < .01), the median size of the outbreak decreased from 24 cases (range:6-146) to 21 cases (range:10-93) (P < .01), and the incidence rate also decreased from 2.01/100 to 1.33/100. The proportion of cases with high fever, severe rash and complications in the BV group was lower than that in the primary varicella (PV), and the differences were statistically significant. The incidence rate of varicella among students who had post-exposure prophylaxis (PEP) activities was 1.42% (488/ 33,878), and 1.63% (2468/ 148,943) among those who did not (p = .005). The single-dose varicella vaccination was less effective in controlling the outbreaks, and the success of the full implementation of the routine two-dose varicella vaccination plan in the pilot cities provided a basis for implementation in the whole province, and long-term follow-up studies are needed to evaluate the effect of the new strategy in the future.