An Epidemiological Survey For Adult Japanese Encephalitis And The Health Economic Evaluation For Vaccination In 2 Prefectures, China

Japanese Encephalitis (JE) is a mosquito-borned viral zoonosis. Usually, children <10 years of age are easy to be infected. After the polio-free period, JE is the leading cause of disability of the nervous system due to the viral infection.With the wild use of JE vaccines, the age distribution was changed in some endemic areas, the proportion of JE cases in older children and adults increased. In July 2006, a JE outbreak was occurred in Yuncheng, Shanxi Province. Most of the JE case were the elder, and had the higher fatality rate, which absorbed much attention from both health systems and society.Due to lack of systematic and complete information of the incidence, fatality rate of adult JE, and no experience for the adult JE prevention and control we could learn from, Therefore, the questions of how to describe the epidemiology and how to prevent and control for the adult JE cases, should be solved.In this study, we selected 2 prefectures, Zibo in Shandong province and Luoyang in Henan province. We conducted an active, population and JE laboratory testing based Acute Encephalitis Syndrome (AES) surveillance, to find the AES incidence in Zibo, and Luoyang, and the age-specific JE incidence, especially the JE incidence in adult population. We collected the direct costs and indirect costs of the JE cases in the acute period, and followed-up the JE cases occurred in 2009, investigated the sequelae, and the direct and indirect costs due to the sequelae within 1 year of discharge. We conducted a case control study for the laboratory-confirmed JE cases in year 2009 and 2010 to find the risk factors and high-risk population, i.e., maybe it is the population need intervention. We collected the EPI program cost from each EPI units, and calculated the operational cost per EPI dose vaccine. We build a Markov model, using a 100,000 adult population cohort to simulate the effectiveness of JE vaccination, calculate the cost-effectiveness, cost- benefit and cost- effectiveness results.We found AES incidence rates were 11.03/100,000 to 13.46/100,000 for the whole population in Zibo and Luoyang. JE incidence was 1.20/100,000 to 2.57/100,000 for the adults aged≥40 years. Compared with the young cases, JE cases higher than 40 years of age had the severe clinical symptoms and higher fatality.From the case-control study, we found the incidence of peasants was 1.86 times than that of non-peasants. If fixed other factors, the risk for feeding pigs in house or in neighborhoods was 21.32 times than without feeding pigs. No matter the single-factor analysis, or multi-conditional Logistic regression analysis, the variables associated with the JE disease, were living in rural areas, peasants, feeding pigs in house or in neighborhoods and so on.If we vaccinated a 100,000 adult population cohort with 2 doses of JE vaccines, could reduce the 48.8 JE cases,12.2 deaths, and 14.6 disabilities, reduce 164.9 DALYs, and reduce 4,944,635.5 RMB yuan for the JE disease.The program cost was 84,322.9 RMB yuan per JE case saved, and the program cost was 24,945.1 RMB yuan per DALY saved. From the perspective of the health system, the cost-benefit ratio of 4.59:1, net benefit was -3,217,327.4 RMB yuan, was not cost effectiveness, however, from the perspective of the whole society, the cost-benefit ratio of 0.83:1, net benefit was 831,355.1 million, was cost-effectiveness.Two variables, the 2nd dose of vaccine and the incidence of JE, had great effects on the model. In the best-case scenario (select high value of incidence, adminster 1 dose of JE vaccine, high value of vaccine effacy and lower value of discount rate) shows that the cost per JE case saved was 25,519.8 RMB yuan and the cost per DALY saved was 4,686.7 RMB yuan. From the health system perspective,1 dose vaccination was very cost-effective with a net benefit of 55,880.7 RMB yuan.The study shows that the incidence of JE in adult was lower than that in children at the era with no JE vaccine, but was higher than that in the local children at present. The clinical symptoms of the JE cases were more serious in≥40 years group than that in≤40 age group. The prognosis of adult cases of JE was worse than young JE cases.For the general adult population, from the perspective of society, JE vaccination was cost-effective and met WHO criteria of "very cost-effectiveness", but from the perspective of the health system, it was not cost-effective. If we only select the population of peasants, or other high risk population, such as feeding pigs in house or in neighborhoods, to give the JE vaccination, we can get the cost-effective results either from the perspective of the health system or from the whole society. We recommended adminster 1 dose of JE vaccine with no charges to the adults living in the rural areas where had the higher adult JE incidence, especially to the adults had pigs in house or in neighborhoods.This study defined the incidence of adult JE cases and analyzed the population should be administered JE vaccines, and evaluated the cost-effectiveness of the vaccination program. This study could give useful information to other countries or regions for the adult JE cases control and prevention.