日本腦炎是台灣地區重要的病毒性腦炎之一，每年的五至十月是流行季節。雖然預防接種普及使病例數明顯下降，但病例年齡卻逐漸提高至以10歲以上的青年或成年人為主。由於疫苗抗體有自然衰退現象，且可能因為自然感染不足的緣故，抗體陽性率最低的年齡層約為20~40歲，因此本研究乃以距離預防接種已有一段時間，但自然感染補強可能不足的大學生為對象，檢測對日本腦炎中和抗體的含量。本研究根據日本腦炎病毒中和抗體盛行率與野外病毒株的分離情形，以台北市、苗栗縣、南投縣與台南縣等四地區大學生為目標族群，對相同對象於流行季節前後分別抽血，檢測對疫苗株與對近年分離野生株的中和抗體的效價。流行季前共有男性113名女性167名接受檢測，而流行季後則分別回收男性73與女性138名樣本。以溶斑減少中和抗體試驗進行檢測，採用溶斑減少70%以上為抗體陽性判定標準，結果顯示大學生日本腦炎中和抗體：(1)對疫苗株的陽性率與幾何平均效價均較對野生株高，(2)不同居住地區個體之抗體陽性率在統計上有顯著差異，但在具有抗體的個體中，抗體強度差異與居住地區無關，(3)在感染季節後未發現效價提昇達四倍的受試者。本研究結果顯示日本腦炎疫苗預防接種的影響力仍及於大學階段。然而推測由於個體的接種經驗，致使對Nakayama疫苗株的中和抗體效價遠高於對野生株的中和抗體效價。在評估該年齡層大學生是否具備中和野生株病毒的抗體時，亦宜考慮以北京株進行。 Japanese encephalitis (JE) is an important encephalitis in Taiwan. The endemic season is from May through October. It is caused by a flavivirus. In Taiwan, the major amplification host of JE is pig. It is transmitted from animal to human via mosquito bite. Many factors were known to affect the protection efficacy of one？HHHHHH？HHHHHHs neutralizing antibodies. Among these factors, sufficient number of vaccination, time after the latest immunization, antigenic heterogeneity and the frequency of natural infection are of the most important. Because of the mass vaccination program starting from 1968 in Taiwan, in the past 30 years dominant population of JE confirmed case has gradually shifted from children to those more than 10 years old. Recently, the lowest positive rate of neutralizing antibody was observed among people of 20-40 years old. Therefore, the capability of college students to neutralize JE virus became one of the most concern topics in public health. This project was conduct to compare positive rates and titers of neutralizing antibodies against one JE vaccine strain (Nakayama) and two JE wild strains (CJN and TN207) among college students. Antibodies titers before and after prevalence season were also compared. Four residential areas in this study were selected according to the prevalence of JE in pig. One hundred and thirteen male and 167 female volunteers were enrolled in this study. All are college students of 19~22 years old. After prevalence season, blood samples of 73 male and 138 female among these volunteers were collected. Titers of antibodies in blood samples before and after prevalence season were analyzed by plaque reduction neutralization test (PRNT), with 70% of plaque reduction as the criteria of seropositivity. Seropositive rates against Nakayama strain were higher than that against two wild JE strains. Seropositive rates among different residential areas were significantly differed. However, titers of neutralizing antibodies were found not different among the residential regions. Four times of booster in neutralizing titer were not observed after the prevalence season. The results indicated that the protections of 4-doses vaccination in college students born in 1981~1984 were still observed. However, their immune responses against vaccine strain were significantly stronger than that against wild JE strains. It might be better on consider of using another JE strain ？HHHHHHXBeijing, to evaluate the efficacy of neutralizing antibodies against wild JE strain for these people.