COVID-19 in Europe and travel: Researchers show the important role of newly introduced lineages in COVID-19 resurgence after last summer

Europe saw a resurgence in the virus after the initial wave of SARS/CoV-2 infection in spring 2020. This was followed by a second wave in late summer. While it is clear that travel played a major role in the spread of the virus, it is still difficult to determine how this may have affected the structure and reinvigorated the epidemic in different European countries.Philippe Lemey – Rega Institute at KU Leuven, Simon Dellicour – SpELL, Spatial Epidemiology Lab at Universit Libre de Bruxelles and their collaborators created a phylogeographic map to determine how new viral lineages (as opposed to persistent ones) contributed to the resurgence in COVID-19 in Europe. The model was based on epidemiological, mobility and viral genomic data from ten European nations (Belgium. Germany. Italy. Netherlands. Norway. Portugal. Spain. United Kingdom. Switzerland).The majority of lineages that circulated at the end the summer in most of the countries they studied resulted form new introductions made since June 15. Researchers also found that transmission of newly introduced lineages is predicted by local COVID-19 incidence: countries with a higher summer incidence (e.g. Spain, Portugal and France had proportionately lower active transmission chains following August 15, compared to France, Belgium, Portugal and Belgium.Their results show that introductions to the UK were especially successful in establishing local transmission networks, with a significant fraction of introductions coming from Spain.Imagine a fire. If there are already a lot of fires, adding more won't change the forest's fate. The fire will continue to spread. Simon Dellicour, FNRS Research Associate at ULB, explains that if there are only a few fire spots, then lighting more can increase the violence and speed up the spread of the fire.These results highlight the danger of viral spread via international traveling. Strategies to stop the spread of variants more transmissible or evade immunity must be carefully considered.Pandemic escape strategies such as vaccination programs are a source for optimism. This has sparked the proposal by EU member countries to issue vaccine passports to boost travel and revive the economy. These strategies come with risks when immunizations are not complete. This is likely to be the case this summer for the European population.According to the authors of the study, conditions similar to the ones in their study could be fertile ground for viral diffusion and resurgence. This may also include the spread of variants that can evade immune response triggered by vaccines or previous infections. They believe that future infections will be reduced by a coordinated and unified European strategy to reduce SARS-CoV-2 spread.###