2017年深圳市学校乙型/Yamagata系流感传播动力学研究及防控措施评价

目的探讨2017年深圳市乙型Yamagata系(B/Y)流感在学校暴发疫情中的传播能力,评价疫苗接种和隔离措施的防控效果。方法运用SEIAR动力学模型对暴发现场调查数据进行模拟,计算疫情的基本再生数(R0)评价B/Y的传播能力;设计SEIARV疫苗接种模型和SEIARQ隔离模型,计算累计罹患率(TAR)和暴发持续时间(DO),评价疫苗接种与隔离措施的防控效果。结果 2017年深圳市B/Y流感暴发疫情的R0为5.97(95%CI:3.66~8.28);无干预措施下模拟疫情将持续52 d,TAR为99.57%。模拟单独采取在疫情发生前接种流感灭活疫苗(IIV),当接种比例为30%、50%和70%时,接种三价流感灭活疫苗(IIV3)或四价流感灭活疫苗(IIV4)的TAR分别为80.51%/76.81%、65.07%/58.48%和44.06%/33.77%;模拟单独采取疫情发生后应急接种,当接种比例为30%、50%和70%时,接种IIV3/IIV4的TAR分别为85.94%/82.46%、73.55%/67.03%和57.90%/47.54%;当接种比例≥50%,如采取疫情发生前疫苗接种+隔离的联合干预措施,TAR均<1%;如采取疫情发生后应急接种+隔离,TAR均<5%。结论 2017-2018年流感季B/Y在学校暴发疫情中传播能力较强;无论接种IIV3或IIV4,高覆盖率的疫苗接种结合隔离措施是有效的流感防控措施。

Transmission dynamic of influenza B virus Yamagata lineage and assessment of infection control measures in schools in Shenzhen

ObjectiveTo analyze transmission dynamic of influenza B virus Yamagata lineage and assess the effects of vaccination and isolation measures for the outbreaks in schools in Shenzhen, 2017.MethodsThe susceptible-exposed-infectious/asymptomatic-removed (SEIAR) model was used to simulate the data from field investigation. Then the basic reproduction number (R₀) was calculated to evaluate the infectious ability of the virus. The SEIARV (vaccination) and SEIARQ (isolation) models were developed, then the cumulative incidence rate (TAR) and the duration of outbreak (DO) were calculated to evaluate the effectiveness of vaccination and isolation measures.ResultsAt the end of 2017, the R₀ of the B/Y influenza outbreak in Shenzhen was 5.97 (95% CI: 3.66?8.28); the epidemic would last for 52 days without any intervention and the TAR would be 99.57%. In the context of vaccination with inactivated influenza vaccine (IIV) before outbreak, when the vaccination rate was 30%, 50% and 70%, the TAR after vaccinations with IIV3 or IIV4 would be 80.51%/76.81%, 65.07%/58.48%, and 44.06%/33.77%. In the context of the emergent vaccination after outbreak, when the vaccination rate was 30%, 50%, and 70%, the TAR after vaccination with IIV3 or IIV4 was 85.94%/82.46%, 73.55%/67.03% and 57.90%/47.54%. In the context of combined intervention of vaccination and isolation before outbreak, when the vaccination rate is ≥50%, the TAR would be ＜1%. In the context of combined intervention of emergent vaccination and isolation after outbreak, when the vaccination rate is ≥50%, the TAR would be ＜5%.ConclusionInfluenza B virus Yamagata-lineage has a strong ability to spread in school outbreaks. In the context of vaccination with IIV3 or IIV4, high coverage combined with isolation is an effective prevention and control measure.