COVID-19: viral mutations due to chance, in more than one way

Paris: The emergence of several more infectious strains of the new coronavirus SARS-CoV-2 has worried governments and scientists, who are studying how and why the virus has become more transmissible.

Like all viruses, SARS-CoV-2 mutates to maximize its chances of survival.

When it replicates, tiny errors in its genetic coding are introduced.

Most of them are irrelevant. But some – like the virus variants that appeared recently in Britain, South Africa and Brazil – may give the virus a decisive new advantage.

“When we keep the number of cases high, we maximize the opportunities for the virus to get into weird situations, which might be rare, and most of them might go nowhere,” said Emma Hodcroft. , epidemiologist at the University of Bern.

More cases equals more transmissions, which maximizes the chances of a significant mutation occurring, she said.

“If we keep the number of cases lower, we are essentially narrowing the playing field of the virus.”

Wendy Barclay, a virologist at Imperial College London, said the mutations were the result of several factors.

“It’s a combination of the amount of virus available, the number of times you roll the dice defines what happens, coupled with the environment the virus is in right now,” she said.

It was not unexpected that the new variants would appear after a year of COVID-19 as global immunity levels rise thanks to vaccinations and natural infections, she added.

“In South Africa and Brazil, there was already a fairly high level of antibody response from people infected and recovered from the virus.”

Other experts have expressed doubts that immunity levels directly influence current mutations.

Bjorn Meyer, a virologist at the Institut Pasteur in Paris, said that each mutation was more likely to occur in a single individual, who then passed it on to others.

He explained the possibility of a patient whose immune system was compromised, and therefore unable to clear the virus as quickly as others.

“In this patient there may be something wrong with the response, so the virus can stick around for a long time,” Meyer told AFP.

While the COVID-19 virus typically infects individuals for about 10 days before being neutralized by the body, some studies have shown that some patients can carry it for several weeks or more, which maximizes the window for mutations.

“There is still some level of immune pressure on the virus in this patient and the virus is forced to mutate,” Meyer said.

He said a more transmissible variant would likely not develop until later during the pandemic, as most immunocompromised people had been protected for months and so few would have been infected initially.

But as cases increase, the risk of the virus infecting an immunocompromised patient – and significantly mutating in it – also increases.

Immune problems may also have affected the virus in another way.

According to the French Academy of Medicine, the South African variant “could result from a more intense and prolonged viral replication in people living with HIV” – whose cases are very common there.

While the precise origins of the variants remain to be discussed, scientists are unanimous in saying that their effect requires careful management.

A more transmissible strain of the virus has been blamed on an increase in the number of COVID-19 cases and deaths in Britain.

Although more infectious, there is currently no evidence to suggest that the newer variants are more virulent than other forms of SARS-CoV-2.

“We cannot rule out this risk,” Meyer said.

But with the sanitary and distancing measures currently in place around the world, coupled with vaccination campaigns, the virus’s “selection pressure” is likely to affect transmissibility rather than potency, he added.

One thing is certain: the virus will continue to mutate, which could bring more dangerous variants.

In fact, they may already be circulating.

“And as the total number of cases continues to grow exponentially, it’s not hard to say that more of the worrisome variants have emerged this winter and remain undetected than those that occurred in the fall and are now on. our radar, ”wrote University of Washington biologist Carl Bergstrom. on Twitter.