Covid-19: assumptions about the origin of the epidemic in the USA challenged

A team of American researchers has traced the course of Covid-19 in Europe and North America. As a result, the first contaminations were properly controlled, but the following ones triggered epidemic outbreaks.

THE ESSENTIAL

• Using genomics, computer simulation and travel records, researchers rule out previous hypotheses about the origin of the spread of Covid-19 in the United States
Using genomics, computer simulation and travel records, researchers dispel previous hypotheses about the origin of the spread of Covid-19 in the United States
The first world power would have had two vectors of contamination of Covid-19: one in the East, the other in the West whose origins remain unknown

Could the spread of the Covid-19 epidemic in Europe and the United States have been avoided? An American study breaks down some scenarios explaining the dynamics of this crisis, a work carried out by a team from the University of Arizona (United States) with the support of 13 research institutes in the United States, Canada , in Belgium and the United Kingdom and published on September 10 in the scientific journal Science.

This study combines evolutionary genomics [dynamique du génome et ses interactions entre espèces et individus, NDLR] from coronavirus samples with computer simulations of epidemics, as well as detailed travel archives. “This allowed us to rerun the tape on how the outbreak unfolded and then check the scenarios that emerge in the simulations against the patterns we see in reality.“, explains Michael Worobey one of the main authors of the study.

United States: the tracks of Seattle and Canada ruled out

This method has torn apart two scenarios that have so far been favored to explain the spread of the virus in the United States. The first hypothesis estimates that it would be a Chinese national flying from Wuhan (Hubei, China) to Seattle (Washington, United States), on January 15, which would have caused the Washington State cluster and then its dissemination. Impossible according to the authors of the article. Even though this person has the oldest sequenced Covid-19 genome in the country, it is too different from those that emerged six weeks later in that same state. Scientists rely more on an origin of the cluster by contamination that occurred in early February and before.

Likewise, they dismiss the idea that the Washington cluster was taken by someone from the border state of British Columbia in Canada. Even if these Canadian genomes are older they do not convince researchers because “sequencing errors in these genomes“. Today, they believe that the West Coast in the United States was directly contaminated by a case imported from China since “tens of thousands of American citizens and visa holders traveled from China to the United States even after the ban took effect [en raison de la fermeture de la frontière par les États-Unis début février, NDLR].“

Multiple clusters shut down through testing and isolation

The researchers claim that there was another vector of contamination of the country via the East coast which would have been contaminated by a case imported from Italy. However, they are struggling to explain the origin of this contamination in Europe. Thus, they also ruled out the hypothesis of Bavarian contamination of the European Union. Even if on January 20, an employee of a Bavarian automotive supply company returned from China with Covid-19 and then infected 16 colleagues, it seems that no other case has been identified following these- this. “An impressive response of rapid testing and isolation prevented the outbreak from spreading further.”say the researchers.

“Our research shows that when you do early intervention and effective detection, it can have a huge impact, both on preventing pandemics and on controlling them once they progress.says Michael Worobey. As the epidemic eventually slipped, there were early victories that show us the way forward: comprehensive testing and case identification are powerful weapons.”