北京市实施2剂次水痘疫苗免疫策略后一起小学水痘暴发疫情调查分析

目的 对北京市实施2剂次水痘疫苗免疫策略后发生的一起小学水痘暴发疫情开展调查,分析导致疫情发生的预防接种相关因素.方法 采用回顾性队列研究方法,利用传染病网络直报系统和疫情期间主动监测系统发现水痘病例,回顾调查全校学生水痘患病史和水痘疫苗免疫史,比较不同免疫史学生的罹患率.结果 总罹患率为2.3%(30/1282),其中0剂次组罹患率5.9%(1/17),1剂次组罹患率4.2%(22/527),2剂次组罹患率0.9%(7/738).总体疫苗接种率为98.7%(1265/1282),其中1剂次接种率41.1%(527/1282),2剂次接种率57.6%(738/1282).1剂次组发病风险是2剂次组的4.5倍,差异有统计学意义(x2=14.285,P<0.01),2剂次比1剂次增加77.3%的保护率;2剂次组中接种时间间隔<3年的罹患率为0,间隔4至5年的罹患率为0.9%,间隔≥6年的罹患率为2.7%(x2趋势=6.762,P=0.013).结论 2剂次水痘疫苗保护率较1剂次显著提高.2剂次疫苗长期保护效果仍需进一步定量评价.

Investigation of a varicella outbreak in a primary school after implementation of the 2-doses immunization strategy in Beijing

Objective An outbreak of varicella in a primary school was investigated after implementation of the 2-doses varicella vaccination strategy in Beijing and the risk factors of vaccination were analyzed. Methods Retrospective cohort study method was used. Cases were detected through both infectious disease reporting network and active surveillance system during the outbreak. Varicella disease history and immunization history of all students were surveyed. Attack rate (AR) of different immunization history groups were compared and risk factors were analyzed. Results Overall vaccination coverage rate was 98.7% (1265/1282), of which 1-dose group were 41.1% (527/1282), while 2-doses group were 57.6% (738/1282). The overall AR was 2.3% (30/1282), of which 0-dose group was 5.9% (1/17), 1-dose group was 4.2% (22/527) and 2-doses group was 0.9% (7/738). The AR of 1-dose group was 4.5 times more than 2-dose group and the difference was statistically significant (P<0.01). This meant that 2-doses vaccination had an extra 77.3% effectiveness comparing to 1-dose. For the AR of different interval time in 2-doses group, <3 years was zero, 4-5 years was 0.9% and ≥6 years was 2.7% (x2trends test =6.762, P=0.013). Conclusions The effectiveness of 2-doses varicella vaccination was significant higher than 1-dose. The long-term effectiveness of 2-doses varicella vaccine needs further quantitative evaluation.