Where does the new coronavirus that started the epidemic wave in France come from? At the outset, everything suggested that the majority of cases were linked to China, the epicenter of the epidemic, or to Italy, the first country to have been seriously affected in Europe. But according to a study by the Institut Pasteur, published last Friday, which has yet to be validated by a reading committee, the epidemic which is hitting France hard is rather due to a new strain, whose origin is not necessarily , nor directly, linked to China or Italy.
"We think that these two countries are part of the potential list of origins but we have concluded that the inferences on the geographical origin of the virus were not reliable", warns the virologist Etienne Simon-Loriere, of the Institut Pastor who directed the study, in Marianne.
The study, co-led by virologist Sylvie van der Werf, is based on 97 SARS-CoV-2 genomes collected in France between January 24 and March 24. In addition to these 97 genomes, taken from the northern part of France (Ile-de-France, Grand-Est and Hauts-de-France, where most of the cases are concentrated), three others from Algeria are added.
Travel all over the world
"Our genomic data reveal the predominant circulation of a large clade (a genetic group, editor's note) in many French regions, and suppose a local circulation of the virus by infections not documented before the wave of cases of Covid-19", say the researchers in the study.
Clearly: a majority of the cases studied during the sudden increase in contamination at the end of winter belong to a particular variety of the virus, the geographical origin of which has not yet been determined. They therefore differ from the first cases detected before the famous wave, and would have circulated "silently" in the country from the end of January.
Concretely, the study notes that the very first cases declared in January in France, them, "were directly imported from the Hubei region in China". Other cases declared in the west and east of France before the wave are associated with Italy.
As for the other samples, taken during the worsening of the epidemic, it is more complicated. These belong to another clade. "Several genomes correspond to patients who have recently traveled to Europe, the United Arab Emirates, Madagascar or Egypt," the study said. The genomes collected in Algeria are probably imported from France.
Questions persist
For now, researchers believe they do not have enough information to determine the country or region of the country from which this version of the virus comes. “The estimates […] are not reliable with the data currently available. "
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This is due to the lack of samples taken early enough in Europe, and the variety of samples taken on different dates. It is also impossible to precisely date the introduction of this version of the virus in France.
No worries, however: these differences between the strains remain "tiny" and "have no effect on the symptoms", guarantees Etienne Simon-Lorière. Its overrepresentation in France is linked to chance, and to the fact that the previous infected, belonging to other strains, were quickly isolated.
So, if it does not designate any origin of this new strain, what is the purpose of this study? Note that "the measures that have been put in place to isolate and contain the first detected cases have been effective," says Etienne Simon-Loriere to Marianne.
For the researchers who led the study, these results also show that tests must be generalized in asymptomatic people to be more effective in managing an epidemic. Identifying the origin of viruses in real time "transforms the way we react to emerging infectious epidemics", they defend. An ideal difficult to achieve, when you know that, even at the dawn of deconfinement, several months after the start of the epidemic, the number of tests will probably remain insufficient.
