The emergence in the United Kingdom and South Africa of two new variants of SARS-CoV-2, more contagious according to the first data, is of great concern to the international community. The point on what we know about it.
All viruses mutate. These changes are changes that occur when they replicate each other.
Scientists have observed multiple mutations of SARS-CoV-2 since its onset, the vast majority of which are inconsequential, but some may give it an advantage for its survival, including greater transmissibility.
Detected in November in the UK, variant B.1.1.7, now known as VOC 202012/01, “probably” originated in southeast England in September, according to Imperial College London.
It spread rapidly throughout the UK and has now been detected in dozens of countries around the world, from the United States to South Korea, India, France and Denmark.
Most of these cases are related to the United Kingdom, but for some, no link with the United Kingdom could be traced, proving that this variant has already been established locally. This is what is happening in Denmark, one of the countries that sequence the most samples, where 86 cases have been identified (with an increasing frequency).
Another variant, called 501.V2, is now the majority in South Africa. It was detected in samples dating back to October and was spotted in a few other countries around the world, including the United Kingdom and France.
For both variants, the cases are probably underestimated, according to experts.
These two variants present several mutations, one of which, named N501Y, is at the center of all attentions. It is located on the coronavirus spike protein, a tip on its surface that allows it to attach to the ACE2 receptor of human cells to penetrate them and thus plays a key role in viral infection.
This mutation, called N501Y, is known to increase the attachment capabilities of the virus to the ACE2 receptor.
“There is no clear relationship between commitment to ACE2 and increased communicability, but it is plausible that such a relationship exists,” says the European Centre for Disease Prevention and Control (ECDC).
British variant more transmissible
Several scientific studies, not yet peer-reviewed and based mainly on modelling, conclude that the British variant is much more transmissible. This confirms the initial assessments of the NERVTAG group of researchers advising the UK government, which estimated that transmission is increased by 50 -70%.
Thus, according to calculations from the London School of Hygiene and Tropical Medicine (LSHTM), the British variant would be 50 to 74% more contagious.
For their latest report, released on Thursday, researchers at Imperial College London analyzed thousands of SARS-CoV-2 virus genomes sequenced between October and December. According to two different methods, they conclude that this variant has a “significant advantage” in terms of contagiosity: 50 -75% more contagious, or a virus reproduction rate (R) between 0.4 and 0.7 higher than the usual virus.
Preliminary results for the South African variant also indicate greater transmissibility, but fewer data are available.
However, some experts believe that there is not enough data to assess with certainty the contagiosity of both variants.
“We have to stay careful. The result in terms of incidence is a combination of factors that combine the characteristics of the virus but also the prevention and control measures put in place” (distancing, wearing the mask, closure of establishments receiving the public…), told AFP Bruno Coignard, director of infectious diseases at the French health agency Public Health France.
“There is no information on the fact that infections with these strains are more serious,” notes the ECDC. But the risk “in terms of hospitalizations and deaths is high”.
“Who says greater transmissibility possibly means a much higher incidence, and therefore even at equal lethality, a greater pressure on the health system,” says Bruno Coignard.
A variant of SARS-CoV-2 “50% more transmissible would pose a much bigger problem than a 50% more deadly variant,” says British epidemiologist Adam Kucharski on Twitter, a statistical demonstration in support.
With a reproductive rate of 1.1, a mortality rate of 0.8%, and 10,000 people infected, it would result in 129 deaths within a month, he explains. If the rate ofmortality is increased by 50%, the number of deaths would reach 193. But if the transmissibility rate increased by 50%, 978 deaths would be to be regretted.
The impact would be very noticeable in countries where even a small increase in transmissibility would shift the reproductive rate above 1, accelerating the epidemic.
The British variant is “really the concern of the moment” because “it can rush us into an extremely complex situation”, warned epidemiologist Arnaud Fontanet on Monday on the radio franceinfo, epidemiologist Arnaud Fontanet, member of the Scientific Council that guides the French government.
In addition, early studies on the British variant also indicate greater contamination among young people under 20 years of age, which raises the question of whether or not schools should be opened.
Thus, the LSHTM study considers that restrictive measures such as containment in place in the UK in November would not be effective enough to control the epidemic, “unless schools, high schools and universities are also closed.”
Vaccination: a hope?
While the vaccination campaigns that have just begun offer hope to emerge from this global health crisis, some are questioning the ability of vaccines to combat new variants.
For both variants, “there is not enough information available at this stage to estimate (if they pose) a risk to the effectiveness of the vaccines,” says the ECDC.
“In the current state of our knowledge, experts believe that current vaccines will be effective against these strains,” said Henry Walke, of the US Centers for Disease Prevention and Control (CDC), at a press conference Wednesday.
However, the South African variant appears at this stage to raise more questions than the British about vaccine effectiveness.
A specific mutation present in this variant, and not in the British, could theoretically “help him circumvent the immune protection conferred by previous infection or vaccination,” explained Professor François Balloux of University College London on Monday, quoted by the British organization Science Media Centre.
However, there is no indication at this stage that this mutation is sufficient to make the South African variant resistant to current vaccines, has tempered Professor Balloux.
The German laboratory BionTech, originally with Pfizer of the worlds first authorised Covid-19 vaccine, assured him that it was able, if necessary, to provide a new vaccine “in six weeks” to respond to a mutation.
“delay to the maximum” the diffusion of variants
It is “illusory” to think that it can eradicate or completely prevent the spread of the new variants, says Bruno Coignard, noting that the goal is to “delay as much as possible” their diffusion.
Thus, for countries where cases of new variants are not widespread, the ECDC recommends “efforts to slow down the spread, similar to those put in place at the beginning of the epidemic”: testing of people arriving from areas at risk with potential quarantine, isolation and tracing of increased contacts for infected persons, limitation of travel…
It also calls for monitoring the incidence of these variants, notably by multiplying virus sequencing.
Some PCR tests can also give an indication of the presence of the British variant, and then better target sequences, explained Professor Fontanet, according to which “extremely aggressive monitoring” is essential.
At the individual level, “because these variants seem to spread more easily, we need to be even more vigilant in our prevention measures to slow down the spread of Covid-19,” stressed Dr. Walke, referring to wearing the mask, physical distancing, hand washing and ventilation of closed spaces, not forgetting to avoid the crowd.