Covid-19: le variant Omicron

The Omicron variant is a new version of SARS-CoV-2 (the coronavirus causing Covid-19) which was identified at the end of November in Botswana, then in South Africa. Its particularity is its high number of mutations compared to the initial strain of the virus, known as Wuhan, and the previous variants, such as the Delta, which has largely dominated global contamination since the summer of 2021. We do not know precisely where and how Omicron appeared. A hypothesis seduces many scientists: the virus would have gradually mutated quietly in the body of an immunocompromised person, a process which would have taken several months to lead to a version clearly different from the initial strain. This new variant is obviously very contagious. It is spreading “at a rate that we have never seen with any other variant” and “is probably found in most countries”, warned in mid-December Tedros Adhanom Ghebreyesus, director general of the World Health Organization. (WHO). South Africa and its neighbors have seen a surge in Covid cases with the arrival of Omicron, which has also seen a meteoric rise in several European countries. This is the case of Denmark and the United Kingdom. More broadly, Omicron could be dominant in Europe by mid-January, according to European Commission President Ursula von der Leyen. Will it definitely replace Delta? It is a strong probability but the scientists evoke other possibilities: that Omicron supplants its predecessor for a time but ends up giving way to it again or that the two variants coexist as is the case for certain strains of the virus of seasonal flu. Cause for concern: Omicron mutations are likely to significantly reduce antibody immunity against the virus. Consequence: it can probably reinfect people previously infected with the virus and contaminate a large number of vaccinated people. Several recent laboratory studies support this last hypothesis. They show that the level of antibodies collapses against Omicron in people vaccinated with Pfizer/BioNTech, Moderna, and even more AstraZeneca or Sinovac. Admittedly, a booster dose seems to significantly boost immunity by antibody, as announced by Pfizer and BioNTech in particular, but we are very far from knowing to what extent this effect lasts over time. However, this does not mean that vaccines lose all their effectiveness. Because antibodies are only one of the components of the immune response, which also involves cells called T lymphocytes. More difficult to measure, this “cellular immunity” nevertheless plays a very important role, especially against the forms serious illness. In fact, a study published in South Africa suggests that the Pfizer/BioNTech vaccine remains rather effective against the severe forms generated by Omicron, including after the first two doses.