New publication in Nature: untangling introductions and persistence in COVID-19 resurgence in Europe

Published on June 30, 2021, by Simon Dellicour

Following the first wave of SARS-CoV-2 infections in spring 2020, Europe experienced a resurgence of the virus starting late summer. Although it appears clear that travel had a significant impact on the circulation of the virus, it remains challenging to assess how it may have restructured and reignited the epidemic in the different European countries. In our new study published in Nature, we built a phylogeographic model to assess how newly introduced viral lineages, as opposed to persisting ones, contributed to the resurgence of COVID-19 in Europe. Their model was informed using epidemiological, mobility, and viral genomic data from ten European countries (Belgium, France, Germany, Italy, Netherlands, Norway, Portugal, Spain, United Kingdom, Switzerland). Our analyses show that in the majority of the countries under investigation, more than half of the lineages circulating at the end of the summer resulted from new introductions since June 15 (illustrated by results reported in Figure 2 of our study). We also show that the success of transmission of the newly introduced lineages was predicted by the local incidence of COVID-19: in countries that experienced a relatively higher summer incidence (e.g. Spain, Portugal, Belgium and France), the introduction events led to proportionately fewer active transmission chains after August 15. Our results illustrate the threat of viral spread via international travel, a threat that must be carefully considered by strategies to control the current spread of variants that are more transmissible and/or evade immunity. Read the whole study here.

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Reference: Lemey P, Ruktanonchai N, Hong SL, Colizza V, Poletto C, Van den Broeck F, Gill MS, Ji X, Levasseur A, Oude Munnink BB, Koopmans M, Sadilek A, Lai S, Tatem AJ, Baele G, Suchard MA, Dellicour S (2021). Untangling introductions and persistence in COVID-19 resurgence in Europe. Nature, in press