Researchers from two leading Belgian universities reveal concerning findings: Over half of SARS-CoV-2 strains circulating in Europe by late summer 2020 arrived after mid-June, largely due to travel. This summer's reopenings raise fears of a Delta variant-driven fourth wave.
Experts have long suspected international travel fueled COVID-19's second wave in summer 2020. A peer-reviewed study from Katholieke Universiteit Leuven and Université Libre de Bruxelles, published in Nature on June 30, 2021, confirms it. In Germany, Belgium, France, the Netherlands, Portugal, and the UK, more than half of strains at summer's end traced back to introductions since June 15.
Now, in summer 2021, eased restrictions have enabled international travel amid rising concerns over the Delta variant. Reports of an even more transmissible "Delta Plus" have surfaced in Portugal and Switzerland. Belgian scientists urge vigilance, citing history.
By analyzing genomic data, researchers mapped the geographical origins of strains introduced post-June 15, 2020. Many hit areas with low prior circulation, igniting rapid spread—like new sparks in a dormant wildfire boosting intensity.
The study links new strain success to local incidence: Higher summer rates correlated with fewer sustained transmissions by mid-August, post-vacation returns.
Vaccination progress differentiates 2021 from 2020, yet lead author Simon Dellicour warns via Belgian outlet BX1: A fourth wave hinges on vaccine uptake and Delta's spread this summer. Caution remains essential, as some variants evade immunity.
