The Omicron variant has spread across the planet faster than any previous variant of Sars-CoV-2 before it. Detected in early November in Botswana, it swept over France in the midst of a wave of contamination by Delta. And it quickly became hegemonic: since February, it has been identified in 100% of the viruses sequenced in Covid-19 cases, according to data from Public Health France.
Almost six months after its discovery, what have we learned about this variant, which has infected millions of French people? To answer this question, franceinfo interviewed several specialists.
A highly transmissible variant…
The speed with which Omicron has supplanted Delta is indicative of one of the major competitive advantages of this variant over its predecessors: its greater transmissibility. As of November 22, 2021, Omicron was detected in barely 0.1% of tests sequenced in France. As of December 27, 2021, it was present in more than 66% of sequenced tests. He had become a majority in just one month. A month later, by January 24, it was in almost 99% of sequenced tests.
Omicron’s arrival coincided with a sudden acceleration of the fifth epidemic wave. From around 50,000 counted in mid-December 2021, the cases counted each day jumped to 365,000 on January 24 before settling at around 90,000 today.
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Part of the explanation lies in the very structure of Omicron, which differs greatly from the original strain of Sars-CoV-2 identified in Wuhan (China). “This variant has about fifty mutations compared to the original virus, including more than thirty in the Spike protein alone”which serves as the key to entering the virus into the body, explains Sandrine Sarrazin, Inserm researcher at the Marseille-Luminy immunology center.
This structural difference with the original strain of Sars-CoV-2 has two consequences. “Mutations that affect the Spike protein make it more active in entering its receptor” and therefore facilitate the entry of the virus into the body, analyzes Matthieu Mahévas, immunologist at the Henri-Mondor hospital in Créteil and at the Necker Children sick institute in Paris. “This could explain why the incubation period seems shorter with Omicron than with the previous variants: you generally become contagious earlier, and probably for less time.”
The second consequence of these numerous mutations concerns the ability of this variant to thwart the protections put in place by our immune system. Vaccines against Covid-19 have indeed been developed to target the original strain of the virus, and are more struggling with this new variant. “We realized in our tests in cell culture that Omicron escaped massively from neutralizing antibodies, whether these come from vaccination or therapeutic monoclonal antibodies that are administered to patients at risk of form severe”explains Olivier Schwartz, head of the Virus and Immunity Unit at the Institut Pasteur.
… but which did not cause hospital saturation
The ability of Omicron to step over part of the defenses acquired by the immune system could have given rise to fears of a great saturation of hospitals, or even a carnage. This catastrophic scenario fortunately did not take place. “The rate of severe forms observed after Omicron infection is very low”observes Olivier Schwartz, who offers a first explanation: “This variant has a tropism that seems different from that of the previous ones: it multiplies strongly in the upper airways such as the nose and throat, and possibly affects the lungs less.”
The epidemic context in which the variant appeared also played a full role. “Omicron emerged in France at a time when the population was mostly vaccinated, or had encountered the virus in the past”, notes Sandrine Sarrazin. If the antibodies produced by vaccination do not prevent infection, they remain very effective in protecting patients against severe forms of Covid-19. “You can see the illustration of this in Hong Kongnotes Matthieu Mahévas. The territory is undergoing a wave of contamination linked to Omicron and which affects an insufficiently vaccinated population, especially among the elderly. This results in a large number of hospitalizations.”
The large proportion of vaccinated people in the French population has therefore made it possible to avoid a hospital tidal wave, but makes “very difficult to objectively assess the intrinsic severity of Omicron”, comments Claude-Agnès Reynaud, director of research at the Necker Institute for sick children. The immunologist would like to point out that the virus is “far from harmless”.
“We welcome a low severity, but more than 100 people die every day in France because of the virus! We become jaded, while the mortality remains very high.”
Claude-Agnès Reynaud, immunologistat franceinfo
Especially since the more Omicron spreads, the more its chances of becoming more formidable increase. “Viruses are not alive: they need our cells to proliferate.explains Sandrine Sarrazin. It is when our cells copy their genome that errors can appear and viruses mutate. This is how the BA.2 sub-variant appeared, from Omicron. Even more transmissible, it was quick to take precedence over its big brother: during the week of April 4, it represented 99% of sequenced Covid-19 cases, according to Public Health France.
A still unclear impact in the long term
Will the cascading contaminations linked to Omicron and BA.2 change the dynamics of the epidemic on the territory? Hard to say. “Cases of re-infection with Covid-19 have been documented, but these are people already affected by other variants like Alpha or Delta, and who then contracted BA.1 (the original strain of Omicron) or BA .2. At present, only a few cases of infection with BA.1 and then with BA.2 have been documented in Denmark”observes Olivier Schwartz.
Are we going to see the emergence of new variants or sub-variants? How long does the immunity that prevents infection last? And the one that avoids serious forms? “It’s all still hard to sayanswers Matthieu Mahévas. Especially since there are many hybrid situations: people infected then vaccinated, vaccinated people who were then infected, or infected people without vaccination…”
The question of the long-term consequences of infection with Omicron also remains to be clarified. “Most of the data on ‘Covid long’ relates to people infected when vaccines were not available, or patients whose immune systems did not respond well to vaccination. Hopefully, this phenomenon is a rarity for people who have responded well to vaccination”explains Claude-Agnès Reynaud.
“There are viruses that some people never get rid of, like the papillomavirusemphasizes Sandrine Sarrazin. After infection, it can remain hidden for ten or twenty years before causing cancer of the cervix, for example. More recently, a study established the role of the Epstein-Barr virus, which causes mononucleosis, in the development of multiple sclerosis. Are such scenarios possible with Omicron? Unlocking these secrets will require further research and time.