The world has been talking about him for a week now. Despite still very preliminary data about it, the Omicron variant has already generated a multitude of hypotheses, both on its ability to escape the immune response induced by vaccination or a natural infection, on its clinical consequences or on its origin.
It is to examine the scientific knowledge – and above all the uncertainties – scientific about Omicron that the epidemiologist Marcel Salathé, president of the management committee of the PNR 78 “Covid-19” of the Swiss National Fund, invited three experts on Tuesday evening Swiss to join him in an audio chat broadcast live on Twitter. An original format that brought together more than 1,500 simultaneous listeners, the content of which we summarize for you below.
Hypothesis n°1: Omicron would be even more transmissible than Delta
The new variant is presented as highly contagious, even more so than the already highly contagious Delta. But be careful to disentangle the hypotheses from the facts, recalled the “Twitterian” panel of scientists. Virologists expect Omicron to be transmitted easily because it has a number of mutations that have in the past conferred better transmissibility to other variants. This is the case of the D614G mutation for example, present in the Alpha, Beta, Gamma and Delta variants.
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But to know with certainty whether Omicron is more transmissible, we will have to wait for epidemiological observations in the field. The fact that the variant appears to be spreading rapidly in South Africa supports this hypothesis.
“However, we must remain cautious, warned epidemiologist from the University of Bern Christian Althaus. The coronavirus had a low incidence in South Africa in recent weeks, so it is possible that these preliminary epidemiological observations are due to random events such as super-spreading situations which may not have long-term consequences. It seems that a clear trend is emerging in the province of Gauteng [where Omicron has been identified], but we must look at what will happen elsewhere in the world because one region alone is not enough to draw conclusions.
Hypothesis #2: Vaccines will be less effective against Omicron
This is one of the most pressing questions following the emergence of the variant. With the selective advantages it has acquired, can it now escape vaccine immunity, even in part?
"The fact that there is some immunity in South Africa puts selection pressure on the virus," said Christian Althaus. Faced with this immune threat, the virus must mutate or it is doomed to disappear. In other words, putting immune pressure – especially partial – on the virus can lead to the selection of characteristics allowing it to escape it.
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As with the issue of transmissibility, Omicron has mutations already identified as conferring immune evasion capabilities to other variants. This is the case of the K417N mutation, already seen in Beta and Gamma.
But here again, caution is in order, recalled Volker Thiel, virologist specializing in coronaviruses at the University of Bern and member of the scientific task force: “The variety of immune statuses, coupled with the low number of cases mean that we cannot say anything about the behavior of the virus in the face of vaccines. Maybe it's even less pathogenic, maybe the T-cell immunity will still be enough to neutralize it… The bottom line is that current vaccines are so effective that they're going to keep us protect, at least in part. This may be what will make the difference between a mild form and a severe form, or between a severe form and death.
Hypothesis 3: The coronavirus would have evolved by varying Omicron through an immunocompromised patient
"Several avenues are possible to explain why the Omicron variant has so many mutations," said Volker Thiel. One of them is that the Omicron variant could have emerged through prolonged infection with SARS-CoV-2 in an immunocompromised individual. The probability for the virus to undergo mutations is in fact all the greater the longer it persists in the body, as is the case in people whose immune defenses are greatly weakened, either due to a state of immunosuppression resulting from an HIV infection, or linked to the taking of immunosuppressive treatments.
This track had, moreover, already been mentioned during the emergence of the Beta variant, also identified for the first time in South Africa.
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Other factors can however explain the emergence of a variant presenting such a constellation of mutations: “It all depends on the selection pressure which is applied to a virus, specified Volker Thiel. Right now, SARS-CoV-2 is facing an ever-changing environment. It began to spread in a naïve population on an immunological level, now it faces people who have been vaccinated for more or less a long time, immunocompromised individuals, others who are cured... To survive, the virus must react to the selection applied to it.
Hypothesis n°4: The Omicron variant would generate milder symptoms
Several South African doctors have reported in recent days seeing covid patients with mild symptoms, not requiring hospitalization. Speaking to Agence France-Presse, Angelique Coetzee, who is also president of the South African Medical Association, recounted the unusual clinical signs: “What brought them to my office [in Pretoria], c is an extreme tiredness”. The majority of his patients were young, men under the age of 40, just under half of whom were vaccinated. In addition to fatigue, they suffered from body aches, a dry cough or "a scratchy throat", she detailed. Only a few had a low fever. Night sweats have also been reported in other cases.
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Is all this a sign that the Omicron variant causes mild symptoms, and that it would become an endemic virus? Scientists aren't sure. “It is too early to draw conclusions on the severity of Omicron because the cases go back at most to a few weeks, and in a young population”, warned Volker Thiel. Young people suffer from covid symptoms much less frequently, and severe cases do not appear until several weeks after the initial infection anyway, while Omicron has only recently been identified.
As for travelers who have contracted the variant, this is also a population with an obvious bias since they are generally young, in good health, and financially well-off, added Emma Hodcroft, molecular epidemiologist at the University of Bern. and co-developer of the Nextstrain network, a platform that tracks the evolution of different pathogens in real time. “And even if the symptoms are less severe, it is above all the potential for transmissibility which is worrying, because the figures can rise very quickly, which could ultimately lead to a very large number of people who could be hospitalized. and possibly die."
Hypothesis n°5: The Omicron variant would have been present in Europe before South Africa
With already several confirmed cases in Switzerland but also in many other countries, the Omicron variant is beginning to make its way outside the African continent. But was he present in Europe before South Africa, as several media have claimed since November 30?
The Dutch health authorities have indeed announced that they have found the Omicron variant in a test taken on November 19, but, as we recall, the latter had already been detected on November 11 in Botswana and then on November 14 in South Africa.
“When a new variant is identified, it is possible to analyze the genomic databases linked to SARS-CoV-2 since the start of the pandemic, specified Emma Hodcroft. However, there is no trace of a variant similar to Omicron, which could have reached Europe or the United States already during the summer. There's no evidence to back that up."
How do you know if someone is a carrier of the Omicron variant? You should know that most PCR tests cannot distinguish the Omicron variant from the Delta variant. For this to be possible, the tests must be able to identify a mutation present in the Omicron variant and known as S-gene-drop-out or S-gene-target-failure (SGFT). However, this is not always enough, since the Alpha variant, first identified in Great Britain, or the Beta variant, detected in South Africa, also have this mutation.
As the Alpha variant is no longer actively circulating (the latter having been replaced by Delta), the presence of SGFT may suggest that the sample is indeed related to the Omicron variant, but confirmation by genome sequencing is essential, which may take several days.
“You have to be aware that you cannot sequence all the positive tests, only a certain percentage is subjected to this procedure, explains Volker Thiel. It is therefore possible that the Omicron variant has gone under the radar somewhat, but only for a short time.
Finally, what can we take away from all this?
“The media headlines can be frightening, but you have to keep in mind that we are not starting from zero,” reassured Emma Hodcroft in conclusion before recalling that “we have learned a lot in two years. We know, for example, that SARS-CoV-2 is transmitted through the air, which should encourage us to take measures to make enclosed spaces safer”.
Volker Thiel for his part affirmed that we should not give in to panic because masks, hand hygiene, distancing measures and above all vaccines remain effective, whatever the variant. “The markets must stop panicking at the slightest announcement. We have to get used to the variants.”
The authors of this article evacuate a last hypothesis: we pronounce “Omicron” and not “Omicron”.
