PARIS • The emergence in Britain and South Africa of two new variants of Sars-CoV-2, which are potentially far more infectious versions of the virus, has prompted widespread concern. Here is what we know - and what we do not - about the mutations.
WHAT ARE THEY?
All viruses mutate when they replicate in order to adapt to their environment.
Scientists have tracked multiple mutations of Sars-CoV-2, the virus that causes Covid-19, since it appeared in China in 2019. The vast majority of mutations did not materially alter the virus' virulence nor its transmissibility.
But one mutation - variant B117, which likely emerged in England in September - has now been detected in countries across the world, including the United States, France and India.
Another variant, 501.V2, found in South Africa in October, has since spread to several nations, including Britain and France.
Both have multiple mutations to the virus, most notably on its spike protein - the part of the virus that latches on to human cells and helps it spread.
Specifically, the mutated versions have an altered receptor binding domain known as N501Y, which is situated on the virus' protein spike and which allows easier access to the ACE2 receptor in human cells.
This makes the mutated versions potentially more infectious than other strains.
The European Centre for Disease Control (ECDC) says that while there is "no clear relationship" between enhanced ACE2 binding and increased transmissibility, "it is plausible that such a relationship exists".
ARE THEY MORE CONTAGIOUS?
Several recent studies - yet to be peer-reviewed - have concluded that the British variant of Sars-CoV-2 is likely to be far more transmissible than other strains.
The Nervtag expert committee that advises the British government on disease control has estimated the new mutation to be between 50 per cent and 70 per cent more transmissible.
A team at the London School of Hygiene and Tropical Medicine (LSHTM) concurs, with experts putting increased transmissibility in the 50 to 74 per cent range.
Last week, researchers at Imperial College London released the results of a study into thousands of genetic sequences of Sars-CoV-2 found in Britain between October and last month.
They found that the new variant had a "substantial transmission advantage", with a reproduction rate between 0.4 and 0.7 higher than the unmutated virus.
Preliminary studies on the South African variant have also concluded that it is more contagious than regular Sars-CoV-2.
But Dr Bruno Coignard, head of infectious diseases at France's heath authority Sante Publique France, said the British variant's spread was due to "a combination of factors".
"These concern the virus' characteristics but also prevention and control measures put in place," he said.
ARE THEY MORE DANGEROUS?
There is currently no evidence to suggest that the mutated viruses are any stronger than normal.
But increased transmissibility alone poses an enormous problem, given that a small but consistent percentage of Covid-19 patients require hospital care.
"Increased transmissibility eventually translates to a far higher incidence rate, and even with the same mortality, this means significant pressure on health systems," Dr Coignard said.
Associate Professor Adam Kucharski, an epidemiologist at LSHTM, said a virus that is 50 per cent more contagious would be a "much bigger problem" than one that is 50 per cent more deadly.
He explained how a disease like Covid-19, with a reproduction (R) rate of 1.1 - where each patient infects 1.1 others on average - and a mortality rate of 0.8 per cent, would be expected to produce 129 deaths within a month.
If the mortality rate rose by 50 per cent, the number of deaths would increase to 193. But owing to the exponential growth in cases with a more contagious variant, a disease with a 50 per cent higher transmission rate would see the death toll hit 978.
Professor Arnaud Fontanet, an epidemiologist with France's science council, said the new British variant was "extremely concerning right now".
Initial studies have also concluded that the British variant is much more contagious among young people.
The LSHTM study concluded that lockdowns similar to those seen across Britain in November would be insufficient to stem the new variant's spread "unless primary schools, secondary schools, and universities are also closed".
WILL THE VACCINES STILL WORK?
As vaccination campaigns get under way across the world, is there any reason to fear that the new mutations may not respond to the host of vaccines already on the market?
After all, the messenger RNA vaccines developed by Pfizer and Moderna trick the body into reproducing the virus' spike protein - the precise part of the pathogen that has mutated in the new versions.
The ECDC said it was too soon to know if the mutations will impact vaccine efficacy.
Last week, Dr Henry Walke from the US Centres for Disease Control and Prevention said that "experts believe our current vaccines will be effective against these strains".
But on Monday, Dr Francois Balloux, professor of computational systems biology and director at University College London's Genetics Institute, said the South African variant's spike protein mutation "helps the virus to bypass immune protection provided by prior infection or vaccination".
German vaccine developer BioNTech has said that if needed, it could develop a new vaccine that would work on mutated versions within six weeks.
WHAT CAN WE DO ABOUT THE NEW VIRUS MUTATIONS?
Dr Coignard said it was impossible to eradicate the new viral variants, although the goal from policymakers should be "maximum delay" of their spread.
The ECDC says that in countries currently unaffected by the new mutations, "efforts to delay the spread should mirror those made during the earlier stage of the pandemic". These include tests and quarantining new arrivals, contact tracing and limited travel.
Prof Fontanet advocates "extremely aggressive surveillance" through widespread testing.
"We need to be even more vigilant in our prevention measures to slow the spread of Covid-19 by wearing masks, staying at least six feet apart from people we don't live with, avoiding crowds, ventilating indoor spaces and washing our hands," Dr Walke said.
AGENCE FRANCE-PRESSE