Case-control Study On The Protective Effect Of Varicella Vaccine

Background and objective: Varicella is caused by varicella zoster virus,which is highly contagious and common in children.Many epidemiological studies show that chickenpox is the first major disease that causes public health emergencies in schools.Schools have been hit hard by the chickenpox epidemic,and school-age children should be the focus of epidemic prevention and control.Vaccination against chickenpox can effectively prevent the disease.At present,the immunization program of chickenpox vaccine in China is 1 dose for children aged 1 to 12 years old.However,a number of studies at home and abroad show that the protective effect of chickenpox vaccine decreases with the passage of time,and breakthrough cases are increasing.Many developed countries have included two doses of varicella in their recommended vaccination programme.To analyze the protective effect of varicella vaccine for children in kindergartens and primary schools,and to explore the rule that the protective effect of one dose of varicella vaccine decreases with time.Based on the results of the study,suggestions are made for the formulation of vaccination strategies for varicella vaccine in Wuxi area.Materials and methods: This study is a case-control study.The reported cases of children in kindergartens and primary schools in Wuxi City from 2017 to 2018 are selected as cases.According to the 1:2 proportion,students in the same or adjacent classes who are not ill are selected as controls.The epidemiological survey is conducted by researchers.The demographic,history of varicella vaccination and clinical symptoms are collected.The exposure of the case group and the control group to varicella vaccination is analyzed.To explore the protective effect of varicella vaccine and the rule that the protective effect of one dose of varicella vaccine decreases with time.Result:1.A total of 942 cases including 324 cases are included in the study.618 controls are collected according to the matching principle.The age distribution of the respondents ranges from 1 to 15 years old,mainly in kindergartens and lower grade student,showing a bimodal distribution.In the case group,there is a significant peak between the ages of 3 and 7,then decreases,slightly increases between the ages of 9 and 11,and gradually decreases after the age of 12.The onset time mainly concentrates in spring and winter,showing a clear bimodal distribution.2.Among 324 cases of varicella,138 cases are breakthrough cases,accounting for 42.6% of the total cases;186 cases are not vaccinated,accounting for 57.4% of the total cases.There are statistical differences in fever,rash number and scab formation time between the two groups.The fever degrees,rash number and scab formation time of the non-vaccinated cases are higher than those of the vaccinated cases,but there are no statistical differences in fever or not,herpes and pruritus between the two groups.3.Among 324 cases of varicella,138 cases are vaccinated with varicella vaccine.Among 618 controls,319 cases are vaccinated with varicella vaccine,and the total protective effect of varicella vaccine is 55%.The protective effect of one dose of varicella vaccine is 26.6%,and that of two doses of varicella vaccine is 67.8%.The protective effect of one dose and two doses is statistically different.4.A total of 457 people are vaccinated with varicella vaccine,of which 421 are vaccinated only once.Of the 421 patients,132 are breakthrough cases.According to the time interval from vaccination to onset time(investigation time),the protective effect of varicella vaccine in 0-1 year,1-2 years,2-3 years,3-4 years and more than 4 years after vaccination are 79.3%?52.7%?33.0%?26.9% and 13.6%,respectively.The protective effect of varicella vaccine decreases with time.5.The result of multivariate Logistic analysis shows that the time of inoculation is a risk factor for chickenpox.With the extension of inoculation time,the risk of chickenpox is on the rise,that is,the protective effect of varicella vaccine is on the decline with the time of inoculation.Conclusion: 1.The total protective effect of varicella vaccine is 55%,the protective effect of one dose is 26.6%(95% CI: 3.3%-44.3%)and that of two doses is 67.8%(95% CI: 21.3%-86.9%).The effect to prevent diseases of one dose of vaccine is poor.It is advocated that two doses of varicella vaccine be vaccinated to improve the effect of diseases prevention and control.2.The protective effects of 0-1,1-2,2-3,3-4 and more than 4 years after vaccination are 79.3%,52.7%,33.0%,26.9% and 13.6% respectively.The protective effect of one dose of varicella vaccine decreases obviously with time,and one dose of varicella vaccine should be strengthened after three years of vaccination.3.After receiving varicella vaccine,even if infected by varicella virus,the symptoms,signs and complications can be avoided,which has a good protective effect.