Epidemiology: Travel implicated in the spread of a SARS-CoV-2 variant in Europe in 2020

The resumption of travel in Europe from June 2020 may have contributed to the rapid spread of a new SARS-CoV-2 variant in Europe over that summer according to research published online in Nature. The study indicates that the new variant 20E (EU1), which is thought to have emerged in Spain, was introduced hundreds of times in European countries by summer time travellers. Although the variant shows no evidence of increased transmissibility, the findings demonstrate how travel can contribute to an increase in variant frequency and highlights the importance of genomic surveillance and containment strategies as travel resumes.

SARS-CoV-2 has been tracked in near real time through the analysis of viral genome sequences, a monitoring method that can also detect the emergence of new variants. In early summer 2020, a new variant was detected in Spain and this variant subsequently spread around Europe, Emma Hodcroft and colleagues report. The variant — named 20E (EU1) — harbours a mutation in the spike protein domain (a structure that mediates the entry of the virus into host cells). However, this mutation does not seem to have a notable effect on transmissibility.

To determine how this variant became a major source of COVID-19 in Europe in the autumn of 2020, the authors traced its evolutionary history, or phylogeny. Their analyses reveal that 20E (EU1) was most prevalent in Spain in July and August, but was observed in many European countries by the end of August, including Belgium, Switzerland, France, Denmark, the UK, Germany, Latvia, Sweden, Norway and Italy. The phylogenetic tree indicates that there were repeated exports from Spain and the patterns of introductions into other countries are consistent with those predicted by travel data. Many EU countries resumed travel around mid-June, which peaked during July and August, coinciding with the peak in 20E (EU1) prevalence in Spain. Thus, the authors propose that international travel, along with insufficient containment and quarantine, had a role in the resurgence of cases in many European countries. Improvements to strategies to reduce the risk of variants spreading as travel resumes are needed to help countries to maintain low levels of SARS-CoV-2 transmission, they conclude.