The Impact Of Different Varicella Vaccination Strategies On Varicella In Guangdong Province

BackgroundVaricella is an acute infectious disease caused by varicella-zoster virus infection,which imposes heavy burdens on societies with the growing incidence.Vaccination is the most effective way to protect susceptible children from varicella.In 2017,Guangdong Province adjusted the self-funded strategy of varicella vaccination from one dose to two doses.And then,Shenzhen further included two doses of varicella vaccine in the routine immunization program in 2019.However,the impact of these two varicella vaccination strategies on varicella remained unclear and needed to be systematically evaluated to ensure their appropriate implementation.Objective and significanceIn this study,four cities in Guangdong Province(Guangzhou,Foshan,Shenzhen,and Dongguan)were selected as research sites.The purpose of this study was to evaluate the protective effect of the 2-dose regimen of varicella vaccine,as well as the changes in the incidence level and trend of varicella before and after the implementation of these two regimens.These results can provide a scientific basis for the formulation of an appropriate varicella vaccination strategy in Guangdong Province.MethodIn this study,the daily data series of varicella cases and varicella vaccination data of Guangdong Province,from January 1,2012 to December 31,2021,were collected.A descriptive analysis was conducted to describe the temporal,spatial and population characteristics of varicella cases in Guangdong and four cities(Guangzhou,Foshan,Shenzhen and Dongguan)from 2012 to 2021.The interrupt time series analysis was established to analyze the change in incidence level and trend of varicella and the impact of the implementation of self-funded two doses varicella immunization strategy in four cities.The same analysis was then applied to the free two doses immunization strategy of varicella in Shenzhen.The impact of free two doses immunization strategy on varicella in Shenzhen was explored through the Bayesian Structural Time Serie model,with controlling confounding factors such as the COVID-19 pandemic,long-term trend,and seasonality.The preventable varicella cases and relative protective effect after the implementation of this strategy were collected.Main resultsFrom 2012 to 2021,484,319 varicella cases aged 1-14 years were reported in Guangdong Province,with a relatively high average annual incidence of 2017-2019.The cases were concentrated in the Pearl River Delta region,such as Shenzhen,Guangzhou,and Foshan.The proportion of scattered children decreased year by year,while the proportion of students increased,and the age of onset appears to be trending toward an old age.The characteristics of the incidence of varicella in four cities were similar to that of Guangdong Province.After the implementation of the self-funded two doses strategy(2017 October),the varicella incidence level in four cities decreased.The incidence rate ratio(IRR)of Guangzhou,Foshan,Shenzhen,and Dongguan were 1.14(95%CI:0.96,1.40),0.78(95%CI:0.65,0.96),0.61(95%CI:0.49,0.81),0.63(95%CI:0.50,0.85),respectively.The preventable varicella cases in Guangzhou,Foshan,and Shenzhen were 30.79%(95%CI:23.28%,38.41%),26.51%(95%CI:18.01%,34.44%),31.02%(95%CI:22.54%,39.84%),respectively,with the cases of Dongguan as reference.The increase in varicella incidence of Shenzhen had turned to a decline after the implementation of the free two doses vaccination strategy(2019 November),with an IRR of 0.54(95%CI:0.33,1.42).The relative protection effect of this strategy was 27.89%(95%CI:-1.34%,55.59%),corresponding to 9478 varicella cases averted.ConclusionsThe incidence of varicella in Guangdong Province was still at a high level.Students were the main group of varicella patients,and the age of onset tends to be trending toward an old age.The evidence from Guangdong Province showed that the self-funded two-dose vaccination strategy for varicella was more protective than the one-dose strategy at self-expense.And the protective effect of the free two-dose immunization strategy of varicella was stronger than that of self-funded two doses immunization strategy.It was recommended to strengthen the vaccination of a second dose of varicella vaccine in school-age children and consider including two doses of varicella vaccine in the immunization program.