Can we afford to relax measures during the summer?

After the 1^st wave of infections in springtime 2020, Europe had to deal with an upsurge in the COVID-19 epidemic at the end of the summer. The number of new SARS-CoV-2 infections rose rapidly, causing a 2^nd wave at the end of October. This wave led governments to once again impose drastic public health measures. However, the emergence of new, more transmissible, variants, such as the Alpha (UK) variant, complicated efforts to control the pandemic. Belgian, British and French researchers (at the Rega Institute, KU Leuven, the University of Southampton, and the Sorbonne Université de Paris) have investigated whether the emergence of new variants was the cause of the epidemic’s upsurge.

The researchers carried out phylogeographic analyses, that is, they retraced the genetic origin of the virus according to place. This was done using epidemiological data from 10 European countries. They analysed about 4 000 genomes from SARS-CoV-2 strains circulating between the 29^th of January and the 30^th of October 2020. The model they developed also integrated epidemiological and human mobility parameters, using international air traffic data, Google and Facebook. The scientists were able to estimate that more than half the variants circulating in these countries at the end of the summer of 2020 appeared after the 15^th of June. The emergence of these new variants saw an increase in new infections. It therefore seems clear that the relaxation of sanitary measures during summer 2020, and especially the resumption of travel, was a major factor in the upsurge of the epidemic and the 2^nd wave in the autumn.

So the majority of variants in circulation at the end of summer 2020 had spread through Europe during the summer. While vaccination of the population gives hope that the epidemic can be halted, numbers of people vaccinated are still too low to prevent the relaxation of sanitary measures during summer 2021 from causing a new wave of contaminations in the autumn. Public health measures that limit the virus’ spread worldwide remain the most efficient means of limiting the pandemic.