The Bill and Melinda Gates Foundation, 500 5th Ave N, Seattle, WA 98109, United States.
The London School of Hygiene and Tropical Medicine, Keppel St, Bloomsbury, London WC1E 7HT United Kingdom.
Vaccine. 2023 Apr 6;41 Suppl 1(Suppl 1):A105-A112. doi: 10.1016/j.vaccine.2021.08.064. Epub 2021 Sep 2.
Circulating vaccine-derived poliovirus outbreaks are spreading more widely than anticipated, which has generated a crisis for the global polio eradication initiative. Effectively responding with vaccination activities requires a rapid risk assessment. This assessment is made difficult by the low case-to-infection ratio of type 2 poliovirus, variable transmissibility, changing population immunity, surveillance delays, and limited vaccine supply from the global stockpile. The geographical extent of responses have been highly variable between countries.
We develop a statistical spatio-temporal model of short-term, district-level poliovirus spread that incorporates known risk factors, including historical wild poliovirus transmission risk, routine immunization coverage, population immunity, and exposure to the outbreak virus.
We find that proximity to recent cVDPV2 cases is the strongest risk factor for spread of an outbreak, and find significant associations between population immunity, historical risk, routine immunization, and environmental surveillance (p < 0.05). We examine the fit of the model to type 2 vaccine derived poliovirus spread since 2016 and find that our model predicts the location of cVDPV2 cases well (AUC = 0.96). We demonstrate use of the model to estimate appropriate scope of outbreak response activities to current outbreaks.
As type 2 immunity continues to decline following the cessation of tOPV in 2016, outbreak responses to new cVDPV2 detections will need to be faster and larger in scope. We provide a framework that can be used to support decisions on the appropriate size of a vaccination response when new detections are identified. While the model does not account for all relevant local factors that must be considered in the overall vaccination response, it enables a quantitative basis for outbreak response size.
循环疫苗衍生脊灰病毒（cVDPV2）疫情的传播范围比预期的更为广泛，这给全球消灭脊灰行动带来了危机。要有效地开展疫苗接种活动，就必须迅速进行风险评估。但是，由于 2 型脊灰病毒的病例与感染比例较低、传染性不同、人群免疫力不断变化、监测延迟以及全球疫苗库存供应有限，使得评估工作变得困难。各国应对疫情的范围差异很大。
我们开发了一种短期、地区级脊灰病毒传播的统计时空模型，其中包括已知的风险因素，包括历史野生脊灰病毒传播风险、常规免疫覆盖率、人群免疫力以及接触暴发病毒的情况。
我们发现，与最近的 cVDPV2 病例的接近程度是疫情传播的最强风险因素，并且发现人群免疫力、历史风险、常规免疫和环境监测之间存在显著关联（p<0.05）。我们检验了该模型对 2016 年以来 2 型疫苗衍生脊灰病毒传播的拟合情况，发现我们的模型很好地预测了 cVDPV2 病例的位置（AUC=0.96）。我们展示了如何利用该模型来估算当前疫情暴发的适当应对范围。
随着 2016 年 tOPV 的停用，2 型免疫力持续下降，对新的 cVDPV2 检测结果需要更快、更大范围的暴发应对。我们提供了一个框架，可以在发现新的检测结果时，用于支持对适当的疫苗接种反应规模的决策。虽然该模型没有考虑到在整体疫苗接种反应中必须考虑的所有相关地方因素，但它为暴发应对规模提供了定量基础。
