Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
Swiss Institute of Bioinformatics, Lausanne, Switzerland.
PLoS Pathog. 2023 Aug 10;19(8):e1011553. doi: 10.1371/journal.ppat.1011553. eCollection 2023 Aug.
The SARS-CoV-2 pandemic has led to the emergence of various variants of concern (VoCs) that are associated with increased transmissibility, immune evasion, or differences in disease severity. The emergence of VoCs fueled interest in understanding the potential impact of travel restrictions and surveillance strategies to prevent or delay the early spread of VoCs. We performed phylogenetic analyses and mathematical modeling to study the importation and spread of the VoCs Alpha and Delta in Switzerland in 2020 and 2021. Using a phylogenetic approach, we estimated between 383-1,038 imports of Alpha and 455-1,347 imports of Delta into Switzerland. We then used the results from the phylogenetic analysis to parameterize a dynamic transmission model that accurately described the subsequent spread of Alpha and Delta. We modeled different counterfactual intervention scenarios to quantify the potential impact of border closures and surveillance of travelers on the spread of Alpha and Delta. We found that implementing border closures after the announcement of VoCs would have been of limited impact to mitigate the spread of VoCs. In contrast, increased surveillance of travelers could prove to be an effective measure for delaying the spread of VoCs in situations where their severity remains unclear. Our study shows how phylogenetic analysis in combination with dynamic transmission models can be used to estimate the number of imported SARS-CoV-2 variants and the potential impact of different intervention scenarios to inform the public health response during the pandemic.
SARS-CoV-2 大流行导致了各种关注变体（VOCs）的出现，这些变体与传染性增加、免疫逃避或疾病严重程度的差异有关。VOCs 的出现激发了人们对了解旅行限制和监测策略的潜在影响的兴趣，这些策略旨在预防或延迟 VOCs 的早期传播。我们进行了系统发育分析和数学建模，以研究 2020 年和 2021 年瑞士 Alpha 和 Delta VOCs 的输入和传播。使用系统发育方法，我们估计有 383-1038 例 Alpha 和 455-1347 例 Delta 输入瑞士。然后，我们使用系统发育分析的结果来参数化一个动态传播模型，该模型准确描述了 Alpha 和 Delta 的随后传播。我们模拟了不同的反事实干预场景，以量化边境关闭和旅行者监测对 Alpha 和 Delta 传播的潜在影响。我们发现，在宣布 VOCs 后实施边境关闭对于减轻 VOCs 的传播影响有限。相比之下，增加对旅行者的监测可能是在严重程度仍不清楚的情况下延迟 VOCs 传播的有效措施。我们的研究表明，如何将系统发育分析与动态传播模型相结合，用于估计输入的 SARS-CoV-2 变体数量以及不同干预场景的潜在影响，以便在大流行期间为公共卫生应对提供信息。
