Paris (AFP)
Variants, mutations ... Both anxiety-provoking and very technical, these terms are sometimes a source of confusion for the general public.
Update on what we know and what this implies for the Covid-19 pandemic.
- How many variants?
At this stage, three are considered as "worrying variants", according to the official name of the WHO: those which were first detected in England, South Africa and Japan (but on travelers coming from Brazil, hence its common name of "Brazilian variant").
They circulate respectively in 125, 75 and 41 countries, according to the last point of the WHO.
They belong to this category because of their increased transmissibility and / or virulence, which worsens the epidemic and makes it more difficult to control, according to the WHO definition.
The category just below is that of "variants of interest", whose potentially problematic genetic characteristics warrant surveillance.
For now, the WHO has retained three, initially spotted in Scotland, the United States and Brazil.
"The weeks and months to come will tell us whether they fall into the category of very disturbing variants which spread very quickly, or whether they will remain variants which circulate at low noise," Etienne Simon explains to AFP. Lorière, head of the RNA virus evolutionary genomics unit at the Institut Pasteur (Paris).
All of these variants are classified by family, or "lineage".
Depending on the mutations they have acquired, they occupy a specific place in the family tree of the original SARS-CoV-2 virus.
- What consequences?
In itself, the appearance of variants is anything but a surprise: it is a natural process since the virus acquires mutations over time, to ensure its survival.
"More than 4,000 variants of SARS-CoV-2 have been identified around the world", explain the British health services on their website.
"Most of them have no impact in terms of public health", underlines the WHO.
It all depends on the mutations they carry.
Thus, it is a mutation called N501Y, common to the English, South African and Brazilian variants, which is suspected of making them more transmissible.
And the South African and Brazilian variants carry another mutation, E484K, suspected of reducing the immunity acquired either by a past infection (with therefore an increased possibility of reinfection), or by vaccines.
For the general public, it is difficult to navigate, especially since these variants have very technical names, without international harmonization.
For example, the English variant is called 501Y.V1 or VOC202012 / 01 and belongs to the line B.1.1.7.
The terms "English, South African or Brazilian variants" are therefore more understandable for the general public, but scientists do not like them, because they consider them stigmatizing for countries.
- More contagious?
There is a consensus on this point regarding the three "variants of concern".
But this is only based on epidemiological data for the moment: researchers are observing how quickly these variants spread and deducing how much more contagious they are.
This therefore does not allow us to have a categorical figure, since the results may vary depending on the restriction measures in place in the regions concerned.
For example, based on the different studies, the WHO judges that the English variant is 36% to 75% more contagious.
Several teams of researchers around the world are analyzing the biological characteristics of these variants, in the hope of finding out why they are more contagious.
"There are hypotheses to be studied: perhaps the viral load is higher, that the variant can enter cells more easily or that it multiplies more quickly", declared to AFP Olivier Schwartz, head of the Virus and Immunity unit at the Institut Pasteur, which heads one of these teams.
Researchers at the American University of Harvard have put forward another hypothesis.
According to them, the infection caused by the English variant could last longer: an infected individual would remain contagious for a longer period than with the classic coronavirus, which could therefore require extending the period of isolation.
But this type of research takes time, and it will take several weeks or even months to get definitive answers.
- More dangerous?
This appears to be the case for the English variant.
A study published on March 10 concludes that it is 64% more deadly than the classic coronavirus.
For 1,000 cases detected, the English variant causes 4.1 deaths, against 2.5 for the classic coronavirus, concludes this study published in the medical journal BMJ.
It confirms the first observations made at the end of January by the British authorities.
In addition, based on other work carried out in South Africa, the WHO estimates that the South African variant "increases the risk of death in hospital by 20%".
- How effective are vaccines?
According to several in vitro studies, the efficacy of vaccines is not significantly reduced by the English variant, but seems to be reduced by the South African and Brazilian variants, because of the famous E484K mutation.
However, even though vaccines are less effective against some variants, that does not mean that they are no longer effective at all.
In addition, these studies focus on a single response of the body after vaccination, the production of antibodies: "They do not assess other types of potential immunity, such as the activity of T and B lymphocytes. ", underline American specialists, including the government expert Anthony Fauci, in an article recently published by the specialized journal Jama.
Either way, manufacturers are working on new versions of their vaccine, tailored to the variants.
Moderna announced on March 10 that it had started injecting new generation vaccines to first patients, as part of a clinical trial intended to evaluate their effectiveness against the South African variant.
This adaptation is essential, because "variants against which current vaccines could be less effective (...) will probably continue to emerge", warns the European Center for Disease Prevention and Control (ECDC).
© 2021 AFP