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More contagious, more resistant, more numerous: overview of Covid variants

overview of Covid variants : More contagious, more resistant, more numerous



How many variants?

At this stage, three are considered to be “variants of concern” at the global level, according to the official WHO denomination: those which were first detected in England , South Africa and Japan (but on travelers from Brazil , hence its common name of “Brazilian variant”). As of April 27, they are circulating in at least 139, 87 and 54 countries respectively, according to 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 number of “worrying” variants may vary in each country, depending on the local situation. For example, the United States has five, according to the classification of the American Centers for Disease Control and Prevention (CDC): the three that are globally, plus two others initially spotted in California.


The category just below is that of “variants of interest”, whose potentially problematic genetic characteristics warrant surveillance. For the moment, the WHO retains seven at the global level, against three at the end of March. The last to have joined this circle, Tuesday, is the variant initially spotted in India. It raises concerns because of the rapid deterioration of the health situation in this country. The other “variants of interest” were initially detected in Scotland, the United States, Brazil, France (in the Brittany region) or the Philippines.


Finally, in addition to these two main categories, many other variants are circulating, which the scientific community seeks to identify and evaluate. "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," explains Agence France-Presse Étienne Simon-Lorière, head of the RNA virus evolutionary genomics unit at the Institut Pasteur (Paris). Whatever their status, all 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.


Why do they appear?


In itself, the appearance of variants is anything but a surprise. This is a natural process, as the virus acquires mutations over time to ensure its survival. "All viruses, including Sars-CoV-2, change over time, and this leads to the emergence of new variants, most of which 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 past infection (with therefore an increased possibility of reinfection) or by vaccines.



For the general public, it is difficult to navigate, especially as 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, Brazilian or Indian variants" are therefore more understandable for non-specialists, but scientists do not like them, because they consider them stigmatizing for countries.


More dangerous ?


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.


Based on the different studies, the WHO judges that the English variant is 36% to 75% more contagious. In a point released at the end of March, she also cites a study conducted in Brazil, according to which the Brazilian variant could be 2.5 times more transmissible. The same suspicions hover over the Indian variant, this time because of "the combination of two mutations already known, but not associated so far", notes the scientific council which guides the French government. This characteristic could give it "an increased transmission, but this remains to be proven epidemiologically", underlines the council in a report published Monday.



Other parameters may be taken into account in the deterioration currently observed in India. According to the WHO, it could in part be explained by "large groups of people during cultural and religious festivals or elections", with a lack of respect for barrier gestures.



Several teams of researchers around the world are analyzing the biological characteristics of the main variants, in the hopes of finding out why they seem more contagious. "There are hypotheses to study: maybe the viral load is higher, that the variant can enter cells more easily or that it multiplies more quickly", declares to Agence France-Presse Olivier Schwartz , head of the Viruses and Immunity unit at the Institut Pasteur, who heads one of these teams. But this type of research takes time, and the definitive answers may not be forthcoming. 


More dangerous ?


Again, there is no certainty. It is the English variant that has been the subject of the most research on this point. A study published on March 10 concluded that it is 64% more deadly than the classic coronavirus, confirming initial observations made at the end of January by the British authorities.



But in mid-April, other work led to different findings, showing that this variant did not cause more serious forms of Covid-19. One of these studies, however, focused on patients already hospitalized: it therefore does not allow us to know whether the variant causes more hospitalizations in all infected people.


How effective for vaccines?


According to several in vitro studies and real-life findings, vaccine efficacy is not significantly reduced by the English variant. On the other hand, in vitro studies show that it could be by the South African and Brazilian variants, because of the famous E484K mutation.


The Indian variant raises the same fears because of a nearby mutation (E484Q), even if little data is currently available. A preliminary study made public on April 23 concludes that the Covaxin vaccine (from the Indian laboratory Bharat Biotech) is less effective against this variant than against the historic virus, in terms of antibody production, but that it still offers a protection. An important nuance, which applies to the other variants: even if they make vaccines less effective, this does not mean that the vaccination is no longer effective at all.



These in vitro studies also focus on a single response of the organism, the production of antibodies, but do not assess the other part of the immune response, called "cellular immunity" (which comes from T and B lymphocytes. ). However, an American study published on March 30 provides reassuring first answers. “Even if larger studies are needed, these results suggest that the action of T lymphocytes […] is largely unaffected by the mutations present in the three variants (English, South African and Brazilian, Editor's note) and should offer protection against emerging variants, ”explain the US National Institutes of Health (NIH) on their website.


Either way, manufacturers are working on new versions of their vaccine, tailored to the variants. An essential adaptation, 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).



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watchincalm
watchincalm
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