Covid-19: understand everything about the Omicron variant, which is sweeping over France



► Is Omicron more transmissible than the other variants?

Since the appearance of Omicron in France at the end of November, the new strain of Covid-19 has been replicating at lightning speed. “Where the Delta variant multiplies by two in twelve days, Omicron multiplies every two to three days”, declared the Minister of Solidarity and Health, Olivier Véran, on Wednesday 22 December. Although the share of this variant represents for the moment 20% of the cases detected on the whole of the territory, and “Probably 30 to 35% in Île-de-France”, the minister assures him: “Right after Christmas, Omicron should in all likelihood be the majority in our country. “

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For Bruno Lina, professor of virology at the CHU de Lyon and member of the scientific council, this strong contagiousness could be explained by the numerous mutations of Omicron: “Odetected more than ten mutations. However, until now, the maximum number of mutations observed was three. ” Result : “The virus infects the upper airways a little more easily, and the cells of the lungs a little less”, continues the virologist.

For Pascal Crépey, professor-researcher in epidemiology at the EHESP in Rennes, the great transmissibility of Omicron has another explanation: “In the laboratory, we have seen that the antibodies present in the serum (the liquid part of the blood that remains after coagulation, Editor’s note) of vaccinated or cured people neutralize the Omicron variant less than the previous variants, which makes that it is able to spread in populations that have been immunized. “ According to a study from Imperial College London published on December 16, if a Covid-19 infection confers 85% protection against the Delta variant, this rate rises to 19% for Omicron.

► Is it more dangerous?

The feedback from the field seems reassuring. “In South Africa, the length of hospital stays is four days for an infection with Omicron, compared to double for Delta. In addition, half of the patients do not need oxygen, and they are sent to intensive care less often ”, details Yazdan Yazdanpanah, head of the infectious diseases department at Bichat hospital in Paris and member of the scientific council. An observation qualified by Pascal Crépey: “You have to be very careful: just because it looks like it’s going well in South Africa doesn’t mean it’s going to be fine in Europe. The immune status of the population is not at all the same: they had a beta variant wave that we did not have and they are much younger than us, with a median age of 27 years, against 43 years in Europe. “

Three recently published studies nevertheless attest to a lower virulence. The first, conducted by Imperial College London on 56,000 cases of Omicron and 269,000 cases of Delta detected in England between the 1er and Dec. 14, came to the conclusion that people with the new strain of the virus have a 20-25% reduced risk of going to hospital, compared to the Delta variant. The second, carried out by the University of Edinburgh in Scotland, suggests that Omicron is associated with a two-thirds reduction in the risk of hospitalizations compared to Delta. Thursday, December 23, the British health security agency indicates that patients infected with Omicron have a much lower risk, between 50% to 70%, of being hospitalized compared to the same Delta.

“Even if the figures are reassuring, we can see that we have very different differences depending on the studies. There is therefore still a great deal of uncertainty concerning the degree of severity of the variant ”, nuance Arnaud Fontanet, epidemiologist at the Institut Pasteur and member of the scientific council. Results also tempered by Dominique Costagliola, research director at the Pierre-Louis Institute of Epidemiology and Public Health: “Even if Omicron seems less dangerous, we know that it is much more transmissible. However, it is the product of the two that will send people to the hospital, so it could lead to more hospitalizations. “

► Are the vaccines effective against Omicron?

It all depends on the number of doses performed. According to the studies available on the subject, simple vaccination – that is to say the injection of two doses – would not be sufficient to neutralize the new variant. Imperial College London, for example, estimated that the level of protection in this case did not exceed 20%. A conclusion shared the day before by the Institut Pasteur, after analyzing the blood of people who have received two doses of Pfizer or AstraZeneca vaccines. Results : “Five months after vaccination, the antibodies present in the blood are no longer able to neutralize Omicron. “

With the booster dose, the situation improves. According to French researchers, “UA third booster dose with Pfizer vaccine, or the injection of one dose of vaccine in people with a previous infection, greatly increases antibody levels, to a level sufficient to neutralize Omicron ”. The same should be true for Moderna, reassures Olivier Schwartz, director of the Virus and Immunity Unit at the Institut Pasteur. On December 14, British scientists also evaluated the effectiveness of the booster dose between 71 and 75% in the case of the Pfizer vaccine, two weeks after the injection. Friday, December 24, the High Authority of Health recommends reducing to three months the deadline for the recall, against five months currently.

► Are hospitals at risk of being overwhelmed?

For the time being, Omicron mainly affects the youngest: according to Public Health France, as of December 22, the incidence rate in Paris is nearly 2,000 cases per 100,000 inhabitants among 20-29 year olds. “But once these age groups are reached, the virus will circulate among older people, and then hospitalizations will begin in the weeks to come”, Yazdan Yazdanpanah warns. This situation is all the more worrying given that Ronapreve, a monoclonal antibody used to reduce the probability of being admitted to hospital in the most vulnerable people, would be totally ineffective against Omicron.

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With such a strong broadcast context, which could result in January by “Several hundred thousand” of cases of contamination per day, Omicron will therefore ” to pose problems in the strategic sectors of operation of our company: food distribution, security, energy, transport, communications and health ”, alarm Olivier Guérin, head of the geriatrics pole of the University Hospital of Nice and member of the scientific council. “In England, the contact cases of nursing staff at the hospital are no longer excluded, because the establishments are saturated. In France, we will therefore have to ask ourselves the question of the benefit between maintaining the line of work and the risk of viral spread ”, concludes the scientist.

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