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Two strains of Sars-CoV-2 circulate, and the most virulent represents 70% of infections

A team of Chinese researchers has identified two main types of Sars-CoV-2 coronavirus, responsible for Covid-19. The second variant, better suited to the human population, would be more contagious and more virulent. No reason to worry about scientists, however, who are still working on a vaccine.

Each year, the flu virus is different, which means developing a new vaccine to take into account the mutations undergone by the virus. Should we fear such a scenario for the Sars-CoV-2, responsible for Covid-19, as researchers around the world begin the race to develop a vaccine ? We are not there yet, but Chinese researchers have just published a study showing that two main types of coronavirus circulating, which would explain why some cases are much more serious.

The original strain supplanted by a more virulent strain

According to the research team, which published its work on March 3 in the journal National Science Review, the coronavirus is divided into two types, L and S, which are distinguished by their surface receptors, by which viruses bind and enter human cells. Type S, the origin ofepidemic, would have gradually been supplanted by type L, which would have adapted to thespecies human by becoming more virulent and more contagious. The latter would have taken over the type S since January 2020, as the pressure selective increased on type S. At the present time, type L represents 70% of the cases against 30% for the strain S. The latter would however be in resurgence, because causing symptoms less severe, it is less well identified.

A permanently mutating virus

No wonder all this: viruses are constantly mutating to adapt to their host and the environment. This is called "nucleotide polymorphism" (or SNP for Single Nucleotide Polymorphism), a mutation that differs by only one nucleotide on a base pair. And since the Sars-Cov-2 is a virus ARN, it tends to mutate easily. Chinese researchers have also identified 149 minor variants among the 103 genomes analyzes. These differences may partly explain why some people are more affected than others. Italian researchers had already noticed that the Italian version of the virus was different from the Chinese version. These mutations remain largely insufficient for the moment to speak of the appearance of a new virus, which would be insensitive against a future vaccine against Sars-CoV-2.

Has the virus mutated in Iran?

However, some suspect mutations of greater magnitude. This is for example the case in Iran, where the mortality rate seems particularly high (5.5% against 2 to 3% in the general population). An Iranian pulmonologist, Quoted by The Express, is said to be "taken aback" by the aggressive nature of the disease. " I have the impression that in addition to the coronavirus, patients are affected by a kind of myocarditis (inflammation of heart muscle) viral, because the attack on the heart seems particularly strong and rapid ", Says the doctor. Other professionals confirm that the virus seems more virulent here. But is it because he transferred, or because of the lack of preparation of the health authorities? When in doubt, theWHO has sent a team to Iran, which is expected to be on site next week.

What is certain is that the more the virus circulates, the more likely it is to mutate from one individual to another. Hence the efforts to contain as much as possible the spread of the epidemic.

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