‘The virus is always looking for its next move’: why science is wary of new variants

The researchers tracked coronavirus mutation spent the week reviewing the details of a new variant discovered this month in Botswana.

This is the latest of more than 1,500 recognized strains of the Sars-Cov-2 virus that have emerged since the pandemic began. In a sign of anxiety about the threat posed by new variants, Britain and Israel on Thursday night imposed travel restrictions on a group of South African countries in response to the spike in numbers. abnormally high mutations in the new strain B.1.1.529.

The question of whether a more transmissible, more lethal, or even vaccine-resistant strain can take the place. dominant Delta variant, appeared in India late last year, is one of the issues that keep scientists and health officials on high alert.

“Has Sars-Cov-2 tried all its tricks? You have to be pretty cavalier to believe that,” said Gavin Screamon, an immunologist and head of Oxford University’s medical science division.

Viruses are ever-changing: each replication introduces new errors in the 30,000-nucleotide sequence that makes up its genome.

Normally, these mutations go away, but each comes with the ability to remotely falsify the virus, possibly enabling it to produce a higher viral load that binds easily. with cells in the respiratory tract or evade the body’s immune system.

Before Delta, the biggest threat came from Alpha variant spread rapidly in the UK. Dozens of strains have been classified by the World Health Organization as “concern” or “concerned” variants and given official names in the Greek alphabet, the latest being the Mu variant appearing in Colombia. in January.

Last month, British authorities began monitoring a subvariable Delta that is about 10% more transmissible. Two other Delta descendants, found recently in Canada and Indonesia, share similarities with this strain.

“It’s been almost nothing out of the ordinary since Alpha and Delta appeared in the first place,” said Emma Hodcroft, an evolutionary geneticist at the University of Basel who was one of the first to track the mutations. last year. “But the virus is always looking for its next move.”

There isn’t a single reason why a more deadly variant shouldn’t emerge, although experts agree that a global vaccination campaign has helped slow the mutations.

Prior to the deployment of a vaccine, the virus faced a “simpler immune landscape,” in which most people are susceptible, and “transmissibility is the easiest win,” Hodcroft said. explain.

Now, with global first-dose coverage of more than 53% and around 30 million injections used globally every day, the virus’ next move is to “cut less and dry”. “It can become more contagious or find a way to evade our immune response — or do both,” she says.

Some say the transmission capacity has peaked. Francois Balloux, director of the University of London Genetics Institute, said the R0 – reproduction number in a fully exposed population – of endemic coronaviruses circulating before Sars-Cov-2 topped at number seven. after decades of natural selection.

Since Delta has an R0 of 6 to 7 – more than double that of the original Wuhan strain – the dominant variant may not have “a lot of room to become more contagious in the short term”, he said.

Balloux predicts Sars-Cov-2 will fall into a pattern where it “evolves slowly in a way around the immune system” over the course of a decade rather than “continuously infectious.” Similar long-term evolution can be observed in influenza and seasonal coronaviruses.

A public health digital board warns of a worrying variant in Bolton, northwest England © Oli Scarff/AFP via Getty Images

However, scientists are still concerned about the sudden mutation of the virus, which derails the global pandemic response and vaccinations.

Strain B.1.1.529, which is widespread in South Africa as well as Botswana, has raised concern for this reason, as many of its 32 mutations have been linked to its ability to evade the immune system and spread faster.

According to a person with knowledge of the matter, the WHO convened an emergency meeting on Friday where it is expected to classify the strain as a variant of concern.

Tulio de Oliveira, director of the Center for Epidemiological Response and Innovation in South Africa, said he was “worried” about this variant and that it is responsible for about 90% of the approximately 1,100 registered cases of the virus. Wednesday in Gauteng province. It is unusual, he said, that this strain could be detected by analyzing the results of conventional PCR tests without the use of genetic sequencing.

“The important question that needs to be answered is correctly [variant’s] affect vaccines,” he added.

Slawomir Kubik, a genomics specialist at Geneva-based biotech company Sophia Genetics, stresses that the “health” of a variant can only be judged by how it “spreads in the world” real world”.

“It’s about genes, environment, and luck. . . If you have a ‘beneficial’ mutation but never transmit it, it will never spread,” he said.

Even if the Botswana strain fades away, other strains will emerge. Venky Soundararajan, principal scientist at Nference, a data analytics company, worries that the impact of the implant could force the virus to reduce its “genetic vulnerability,” producing an “escape variant” that could the ability to evade the immune system.

“Vaccines are God-given the ability to prevent infection and serious illness, but they paradoxically also increase our need to track these very specific, targeted mutations,” he said.

Soundararajan warns that the uneven distribution of sequencing technology has created “holes” in genome surveillance. More than 80% of the 5.4 million Sars-Cov-2 genomes uploaded to the Gisaid global repository come from just two continents: North America and Europe.

While no one can be sure where or when a dominant variant will emerge, there is scientific consensus that Delta won’t last forever.

Kevin McCarthy, a professor of microbiology and microbial genetics at the University of Pittsburgh, said the virus’s evolution was “near its peak”, after which the odds were in favor of an escaped variant. .

“Are we going to switch to something where the virus changes its antigenicity and erodes the effectiveness of the vaccine? I think that’s likely to happen,” he said. “If a virus is faced with a binary choice of evolution or extinction, it will evolve.”

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