陕西省麻疹高接种率和高发病率的原因分析

目的探讨陕西省麻疹高接种率下高发病率的病原学和疫苗免疫相关因素。方法分析麻疹病例年龄及免疫史。从咽拭子中分离病毒，用酚-氯仿抽提法提取病毒RNA，逆转录一聚合酶链反应（RT—PCR）扩增N基因-COOH端的450个核苷酸（bp）片段，进行序列测定和基因分型。用微量中和试验测定疫苗免疫血清及麻疹病例急性期血清中和疫苗株和野毒株的抗体水平。结果麻疹病例中有麻疹疫苗免疫史的平均占38．97％；麻疹病例急性期血清：有免疫史的中和S191株GMT（56．18）明显高于H1野毒株GMT（26．90）；无免疫史的S191株GMT（25．40）与H1野毒株（27．86）相近。疫苗免疫血清：S191株抗体效价≤16血清中有19．15％为H1野毒株抗体阴性。结论陕西省近年出现的麻疹高接种率水平下的高发病率现象不排除麻疹流行株变异和疫苗对流行株H1基因组野毒株保护性不足两方面因素。

Study on a high coverage of measles vaccine while high incidence of measles disease still appeared in Shaanxi province

OBJECTIVE: To analyze the affecting factors on the cause of measles and measles vaccine under the high coverage of measles vaccine in Shaanxi province. METHODS: Age distribution and vaccination history on measles cases were studied. Throat swabs were obtained from measles cases. Measles virus was isolated from collected specimens with phenol-chloroform extraction method. Amplification was performed by RT-PCR in order to amplify 450 bp fragment of the -COOH side of N gene,and then the sequences of PCR products were detected to confirm the gene type of measles virus. Sera were obtained from patients who were in acute phase of measles disease,and antibody titer against measles vaccine strain and wild strain were determined by small amounts neutralization test. RESULTS: Measles cases with the history of measles vaccination were accounted for 38.97% of the total numbers. The geometrical mean titer (GMT) (56.18) against S191 attenuated strain was significant higher than that of wild strain (26.90) among these measles patients with history of having received measles vaccination. The GMT (25.40) against S191 attenuated strain was similar to that of wild strain (27.86) among these measles patients with non-history of measles vaccination. The antibody negative rate against wild strain was 19.15% to these sera from patients with the history of measles vaccination and antibody potency against S191 strain was less than 16. CONCLUSION: The appearance of higher measles incidence under the higher coverage of measles vaccine indicated that measles epidemic strain might degenerate as the result regarding the failure of the present measles vaccine in protecting the transmission of H1 wild strain.