Investigation of a varicella outbreak and vaccination efficiency in a kindergarten in Nanjing, Jiangsu
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摘要:
目的 调查南京市一起幼儿园水痘暴发疫情的危险因素和评估水痘减毒活疫苗(VarV)的免疫效果。 方法 确定病例定义并完成病例搜索,收集病例基本信息、临床记录、流行病学史、水痘免疫史等资料,描述病例三间分布特征和罹患率差异。 收集罹患率较高班级全部幼儿的水痘免疫史和水痘患病史,采用回顾性队列研究方法分析接种与未接种疫苗的幼儿间罹患率差异,评估疫苗免疫效果以及不同接种时间间隔对疫苗免疫效果的影响。 结果 共收集61例水痘病例,幼儿罹患率10.87%(59/543)显著高于教职工2.94%(2/68)(χ2=4.22,P=0.040)。 首发病例为一名教职工,发病后仍在岗工作,未被学校常规健康监测发现,也未进行主动报告;其请病假后,校方未采取干预措施。 疫情持续2个月,累计发生5代病例,代间距中位数15 d。 不同班级间罹患率差异有统计学意义(χ2=256.98,P<0.001)。 突破性病例8例(13.11%)均仅接种1剂VarV,接种VarV至发病的时间间隔中位数4.11年。 结果显示,疫苗保护效果为65%(95% 置信区间:24%~84%);1剂次疫苗接种年限> 3年其保护效果下降。 结论 本次报道为一起首发病例为教职工的幼儿园水痘暴发疫情。 未及时发现和隔离病例、教室布局拥挤、疫苗接种覆盖率低及1剂次疫苗接种年限长是疫情发生的可能危险因素。 Abstract:Objective To identify the risk factors for a varicella outbreak in a kindergarten in Nanjing, Jiangsu province, and evaluate the efficiency of varicella attenuated live vaccine (VarV) in the children. Methods Case definition was established and case finding was conducted. The demographic data, medical records, epidemiological history, immunization history of varicella and other data were collected from the cases. The distribution characteristics of cases and the differences in attack rate were explored. The immunization history of varicella and history of varicella were collected from children in classes with a high attack rate of varicella. A retrospective cohort study was used to analyze the differences in attack rate of varicella between vaccinated children and unvaccinated children, and the efficiency of VarV as well as the association between the time interval of the vaccination and efficiency of VarV were evaluated. Results A total of 61 cases of varicella were diagnosed. The attack rate of varicella was significantly higher in children (10.87%, 59/543) than in kindergarten staff (2.94%, 2/68) (χ2=4.22, P=0.040). The index case was a head teacher, who continued to work after the illness onset without reporting and was not detected by the routine health surveillance of kindergarten. The school perform no intervention measures after this teacher's sick leave. This outbreak lasted for two months, resulting in 5 generations of the cases with a median generation interval of 15 days. The attack rates among different classes showed significant difference (χ2=256.98, P<0.001). Among 61 cases, 8 (13.11%) cases were breakthrough cases, who had received one-dose VarV. For these 8 breakthrough cases, the median time interval between vaccination and illness onset was 4.11 years. The results showed that VarV efficiency in this outbreak was 65% (95% CI: 24%–84%), and the vaccine efficiency decreased in the cases with the interval of more than 3 years between the first dose vaccination and this outbreak or illness onset. Conclusion This was a varicella outbreak in kindergarten with index case being a school staff. The potential risk factors for this outbreak included failure to identify and isolate case timely, inappropriate distribution of classrooms, low vaccination coverage, and long time after one-dose vaccination. -
Key words:
- Varicella /
- Disease outbreak /
- Vaccine efficiency /
- Breakthrough varicella
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表 1 江苏省南京市一起幼儿园水痘暴发疫情幼儿病例班级分布
Table 1. Classroom distribution of children infected with varicella in a varicella outbreak occurred in a kindergarten in Nanjing, Jiangsu
类别 病例数(例) 幼儿(人) 罹患率(%) 年级 小班 2 163 1.23 中班 9 148 6.08 大班 48 232 20.69 班级 小4班 1 33 3.03 小5班 1 33 3.03 中2班 1 37 2.70 中3班 4 37 10.81 中4班 4 37 10.81 大3班 16 39 41.03 大4班 22 39 56.41 大5班 5 39 12.82 大6班 5 38 13.16 表 2 水痘的疫苗保护效果与接种时间间隔关系
Table 2. The association between the effectiveness of varicella vaccine and the time interval of vaccination
水痘疫苗接种史 接种时间间隔a(年) 病例数 调查人数 罹患率 (%) RR值 95% CI 疫苗效果 (%) P值 接种 0~3 1 7 12.50 0.29 0.05~1.83 71 0.118 >3 5 28 19.23 0.37 0.16~0.84 63 0.006 未接种 − 37 76 48.68 参考 注:a. 患病幼儿的接种时间间隔(年)= 水痘发病日期-水痘疫苗接种日期;未患病幼儿的接种时间间隔(年)=暴发日期-水痘疫苗接种日期。RR. 相对危险度;CI. 置信区间 -
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