The Immunization Strategy Evaluation And Cost-benefit Analysis Of Varicella Attenuated Live Vaccine In China

BACGROUND Varicella(chickenpox) is an acute and contagious infectious disease with worldwide distribution. In the temperate climate of northern hemisphere, most of the varicella happened among the population younger than10years. The varicella vaccine is the most effective method to control the disease. Before varicella vaccine was introduced, about4million cases of varicella were reported in the United States. During the period of2005and2011, the reported incidence of varicella is3.2to30.13/100000in China. All vaccines in the world are derived from Oka virus strain. Most of the vaccines used in China are made by the domestic factories. From2007, most of vaccine preventable diseases had been included into Expanded Program of Immunization (EPI) in China, which means the possibility of introduction of varicella vaccine into EPI in China.When considering the introduction of a new vaccine into EPI, the analysis of both epidemiological and economic factors is needed to rationally make use of resource of public health and realize the benefit maximization. When considering the varicella vaccine being introduced into EPI, the benefit-cost studies had been made in most of industrialized countries and only one developing country-Brazil.The purpose of our study is to analyze the disease burden of varicella in China, and to set up the epidemiological model to evaluate the possible effect of different immunization strategy of varicella in China, and to study the benefit-cost with different strategy.METHOD In2004, the cost study of immunization per dose of2003had been conducted in three provinces (Shandong, Hunan and Gansu) in China. And the disease burden of varicella of2007(including incidence, inpatient case burden and outpatient case burden) had been invested in the same field in2008. The price of vaccine had been estimated based on the data of market information. The parameters of varicella disease and vaccine were estimated based on the literature review. The infective force and contact matrix information were same as what Halloran used.Based on models of Hechcote and Halloran, we set up our model with more precise parameter and clearer diagram. Base on the age-structure of Chinese population,10situations were defined to simulate the disease natural history of varicella. A serial of differential equations was set up to model each situation. With software of Fortran, the epidemiological characteristic of varicella was described. All the immunization strategies and their benefit-cost ratio were evaluated.RESULT With the assumption of3%of the discount rate, the administration cost per dose is calculated as23.37RMB per dose, the cost of outpatient is555.62RMB per case, and inpatient is4531.14RMB per case in2011in China. The result of population simulation shows that, the birth rate peaked during late1970s and beginning of1990s, and then decreased. The birth rate is0.7%now.After intervention with different strategies, the incidence of varicella decreased distinctly. Among the four candidate strategies, one dose routine immunization shows the lowest decrease of incidence, two dose routine immunization plus campaign strategy shows the quickest decrease of incidence. With the one dose immunization strategy, the breakthrough incidence peaked around20to30years following introduction of the vaccine, and then decreased to low level which is higher than other strategies. After intervention of varicella vaccine with different strategies, the proportion of adult case increases compared with those of none-intervention. But the total case number of adult case is smaller than those without intervention. The epidemiological characteristic can’t be changed if the coverage of vaccine is lower than40%. The disease can be controlled moer effectively with more coverage.The benefit cost ratios of4strategies are all much higher than1. The economic effect of one dose strategy is better than that of two doses.CONCLUSION The disease burden of varicella is heavy in China. The incidence and the disease burden can be decreased efficiently with different strategies, based on the simulation of the model. With the sufficient vaccine production, efficient administration system and the sustained financial support from central government, the introduction of varicella vaccine into EPI is possible.One dose strategy is the best one on the economic issue. The two doses plus campaign strategy is the most effective intervention of varicella virus spreading on the epidemiological issue. Most of additional cost of later strategy is from campaign happened in the next year after vaccine introduction. Considering the two issues and the societal factor, the two doses plus campaign strategy is recommended.