Omicron variant: some certainties and two great unknowns

What do we know about him?

Six weeks after its identification in South Africa, data from several countries converge on two points: Omicron is transmitted much faster than the previously dominant variant, Delta, and seems to cause less severe forms of the disease overall.

Omicron is progressing dramatically in many countries and cases are doubling every two to three days, unheard of with previous variants.

At the same time, data from “the United Kingdom, Canada, the United States and Israel suggest a reduced risk of hospitalization for Omicron compared to other variants (from 56% to 81%)”, underlines Friday the French health agency Public Health France.

This has also been observed previously in South Africa. However, these data are still incomplete and should be handled with caution.

Important point: it is not known if this apparently less seriousness comes from the intrinsic characteristics of the variant, or if it is related to the fact that it strikes populations already partially immunized, by the vaccine or a previous infection.

One thing in particular could partly explain why Omicron is both more contagious and less severe.

According to several studies, it seems to particularly infect the upper airways (nose, throat) but less the lungs, where severe forms of Covid start.

If it remains confined to the upper airways, it can be expelled – and therefore transmitted – – more easily by an infected person.

Be that as it may, its greater contagiousness pushes many specialists to advise the use of FFP2 masks, more protective than surgical ones, in interior spaces.

Consequences on the hospital?

This crucial question remains unanswered, even if things become clearer.

The equation to be solved: will Omicron’s decrease in severity be enough to compensate for the fact that it is much more transmissible?

“Even if the proportion of severe cases is lower, having record numbers of cases can lead to record numbers of hospitalizations,” US virologist Angela Rasmussen said on Twitter on Friday.

However, the consequences for the hospital seem different from those of the previous waves.

If it weighs heavily on hospital beds in general, Omicron seems to saturate resuscitation less, since it causes less serious forms.

This, for example, is suggested by a report just published by the Danish National Health Agency SSI.

In one month, from December 1 to January 1, the number of new cases increased by 69% in Denmark. But this increase does not have such a strong impact on hospitalizations (+ 47%), and even less on critical care admissions (+ 20%).

However, it will take more hindsight to confirm these data. Especially since it is hard to distinguish people hospitalized because of the Covid from those who are hospitalized for another reason, but find themselves suffering from the disease.

What about vaccines?

Omicron’s mutations appear to allow it to reduce antibody immunity against the virus. Consequence: it can probably contaminate a large number of vaccinees, and re-infect people previously infected with the virus.

Several laboratory studies show that the antibody level collapses in the face of Omicron in people vaccinated with Pfizer / BioNTech, Moderna, and even more AstraZeneca or Sinovac, a Chinese vaccine used in around fifty countries.

Encouragingly, a booster dose with Pfizer / BioNTech, Moderna or AstraZeneca seems to clearly boost antibody immunity. But a crucial piece of information is missing: we don’t know how long this effect lasts.

However, the drop in antibodies does not mean that the vaccines are no longer effective. Because antibodies are only one part of the immune response, which also involves cells called T lymphocytes.

More difficult to measure, this “cellular immunity” nonetheless plays a very important role, especially against severe forms of the disease.

Thus, a study presented in mid-December in South Africa suggests that Pfizer / BioNTech remains effective against serious forms due to Omicron, including before the booster and, therefore, probably even more after.

The last wave, really?

With a more contagious but less dangerous Omicron variant, some hope that this wave will sign the end of the pandemic by providing the planet with a large share of collective immunity.

“Perhaps this is the last variant, perhaps this is the last wave, perhaps this wave will allow us to acquire a form of immunity,” French Minister of Health Olivier Véran said on Monday. .

One of the officials at Danish health agency SSI, Tyra Grove Krause, also expressed “cautious optimism about the situation once we get past the Omicron wave”.

However, we must beware of excessive optimism as the future scenarios remain unpredictable.

“The more Omicron spreads, the more it is transmitted and the more it replicates, the more likely it is to generate a new variant,” warned WHO official Catherine Smallwood in a statement to AFP on Tuesday.

It is therefore far from certain that the Omicron wave will be the last. But even if it is not, specialists hope at least that the level of immunity provided by previous infections and vaccines will limit the impact of subsequent ones.

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