While dozens of countries blocked the flow of people and goods from Britain to prevent a new and more contagious strain of coronavirus, scientists rushed to understand how it arose and the extent of its threat.
Here are some of the key questions that are being asked and the answers that have come up so far.
– How often do viruses mutate? –
All the time, but some viruses do it more than others.
A two-dose measles vaccine, for example, can last a lifetime, when the cocktail of flu vaccines changes each year to keep up with the genetic change in shape.
Coronaviruses are somewhere in between, and what has ravaged the world this year, known as SARS-CoV-2, is no exception.
“Viruses are constantly changing through mutation and the emergence of a new variant is an expected occurrence and is not a cause for concern,” the European Center for Disease Prevention and Control (ECDC) said in a report on Sunday. assessment of threats to the new strain.
As for the pathogen caused by Covid-19, “even in March, there were eight large lineages that all separated,” Susan Hopkins, a senior professor of infectious diseases at Imperial College London, told reporters on Monday. .
The most critical question is where these mutations in the virus occur and whether they will make them more infectious and / or deadly.
Prior to the appearance in Britain of this more contagious strain, other genetic variations were mostly benign.
– How has the new strain changed? –
The possibility that a variant of SARS-CoV-2 will find a host to infect is significantly determined by the interface between the so-called ear protein of a virus and a specific receptor on the surface of many human cells known as ACE2.
The easier it is for the virus to attach to a receptor, the more likely it is that an infection will occur.
It is possible that the new mutation, known as the 501Y variant, has changed in ways that increase its chances of successful coupling.
“There is a really unusual cluster of mutations associated with this variant: 22 coding changes throughout the virus genome,” said Wendy Barclay, head of the infectious diseases department at Imperial College London and a member of NERVTAG , a group of scientists. advising the British government on the threat posed by emerging respiratory diseases.
He told reporters, that the mutations observed in the ear protein “would facilitate the entry of the virus into the cells and could biologically explain an increase in transmission.”
The missing pieces of genetic code in other regions, compared to the previous generation of SARS-CoV-2 from which 501Y emerged, could also increase its propagation capacity, he said.
– How much more infectious? –
Announcing stricter blocking measures over the Christmas holidays, British Prime Minister Boris Johnson said on Saturday that the new viral strain “may be up to 70 per cent more communicable than the original version of the disease”.
This assessment was based on preliminary data from sequenced virus genomes collected in London and parts of the south-east of England.
In early November, scientists found that the new variant was responsible for just over a quarter of infections in these areas. In the week ending Dec. 9, it accounted for more than 60 percent of all new cases.
Since Johnson’s crash announcement, which triggered bans on commercial flights and border closures, British scientists have been getting even more data.
“We are now very confident that this variant has a transmission advantage over other virus variants that currently exist in the UK,” said Peter Horby, Professor of Emerging Infectious Diseases at Oxford University and President of NERVTAG.
Recent calculations, he added, suggest that 501Y is 50 to 70 percent more infectious.
Another indicator of its ability to spread is the reproductive number of the variant, or “R rate”: the average number of new cases generated by a single infected person.
Anything above 1.0 means that a virus continues to find new hosts and is spreading through a community, county, or country.
“Even during the (recent) closure in England, this virus had an R number about 0.4 times higher than non-variant strains,” said Neil Ferguson, director of the MRC Center for Global Infectious Disease Analysis and a member of NERVTAG .
“Non-variant strains had an R number of approximately 0.8, but this variant had an R of 1.2 or even higher.”
This could be bad news for efforts to curb the spread of Covid-19, which has already caused more than 67,000 lives in Britain and 1.7 million worldwide.
“I think it’s very likely to become the dominant strain across the UK given the trends we’ve seen so far,” Ferguson said.
The World Health Organization (WHO) said on Tuesday that “the initial analysis indicates that the variant can spread more easily among people,” but said more research was needed to assess its impact on treatments and vaccines.
– Where did the new strain come from? –
Scientists are not sure where the most contagious variant, officially known as SARS-CoV-2 VUI 202012/01, first appeared, but many suspect Britain is zero.
The first known case there was shown on September 20th.
“It’s very likely to show up here, but it’s also likely to do so in other countries,” Hopkins of Imperial College London said.
Denmark, the Netherlands, Australia and Italy have reported cases, he said.
A variant with some of the same genetic deletions has also been identified in South Africa, but is thought to have evolved separately, reinforcing the idea that mutations confer a “transmission advantage.”
It is also possible, scientists say, that the 501Y is already more widespread than previously thought, but it has simply not been detected.
The only way to detect a mutated version of SARS-CoV-2 is to sequence the entire genome of the virus, but Denmark and Britain are the only European countries that do this routinely.
“The UK may be a victim of its own technical success in highlighting the emergence of the 501Y variant,” said London School of Hygiene & Tropical Medicine professor Brendan Wren, who noted that Britain could be treated. ” like the lepers of the world. “
Horby and other NERVTAG scientists said Monday they are unlikely to trace the strain to a “zero patient,” but they have no idea how it could have come about.
“The hypothesis would be that this happened to someone immunosuppressed who therefore had circulating mutations alive for a long period of time,” he said.
– Is the 501Y more virulent? –
“There is no indication at this time of a greater severity of the infection associated with the new variant,” the ECDC said in its threat assessment.
This conclusion, however, “is called into question by the fact that most cases were reported in people under 60, less likely to develop severe symptoms.”
At the same time, “there is an indication that there is a greater propensity to infect children,” Ferguson said.
Even if it is shown to be true, that does not mean the virus is “targeted” at children, who until now were less prone to infection and, when they detect the error, show severe symptoms, Barclay said.
“The previous virus had more difficulty binding to ACE2 and entering (human) cells,” he explained. This made adults, with more abundant ACE2 receptors in the nose and throat, an easier target compared to children.
“If the new strain has an easier time getting into and joining the cells, that would put the kids on a more equitable playing field,” added Barclay, who noted the additional impact of the social mix of young people, especially at school.
– Will the vaccines still work? –
Scientists in Britain and other countries are testing the new strain against the various SARS-CoV-2 vaccines, but so far there is no evidence that they are less effective against 501Y.
“We may need to update the vaccines, maybe not every year,” Barclay said. “But we will have to control that these viruses advance.”
He added that updating the new generation of so-called messenger RNA vaccines will be much easier than modifying flu vaccines, as happens every year.
The two leading vaccines in Europe and the United States (one manufactured by Pfizer-BioNTech and the other by Moderna) are based on RNA.
BioNTech co-founder Ugur Sahin said on Tuesday that it was “very likely” that his vaccine would work against the mutated strain detected in Britain, adding that the company could adapt the vaccine if needed in six weeks.
Researchers are also investigating the possible impact of the new strain on Covid-19 testing and treatments, although so far there is little to suggest that either is significantly compromised.
“We have to be careful in our conclusions, they are still first and there is still a lot of uncertainty about many aspects of this new variant,” said Ferguson, a member of NERVTAG.
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