Covid-19: what we know about XBB.1.5, the most infectious variant ever detected

In France, only 13 cases have been detected, but this figure is probably a huge underestimate (©Archives La Gazette de la Manche)

This is another newcomer to the Omicron family. And XBB. 1.5 cause for concern, as it is spreading at full speed and is already circulating in around thirty countries. According to WHO, this subvariant is “the most contagious that has been detected so far”. The World Health Organization also ensures that it is monitored very closely.

Contagion, virulence, state concern… What do we know about this new sub-lineage.

What are these sub-variants?

XBB.1.5 is a derivative of the XBB Omicron subvariant, which originates from a recombination cross of two BA.2 subvariants.

According to Professor Antoine Flahault, epidemiologist and director of the Institute for Global Health at the University of Geneva, contacted by, “XBB was originally identified and made waves in Asia, India and Singapore last summer, but its XBB.1.5 offspring appears to have emerged in New York.”

Where is it detected?

According to the latest data available (as of January 5), this subvariant has been detected in 29 countries, including the United States since last fall (and now also in South Africa, according to virologist Tulio de Oliveira) . Across the Atlantic, it now represents 40% of published orders. In the UK, where growth is also rapid, it is detected in one in 25 sequences.

France is also concerned, but to a lesser degree:

XBB.1.5 has been detected in 13 patients in France to my knowledge, but this figure appears to be greatly underestimated.

Antoine FlaaultEpidemiologist and Director of the Institute of Global Health at the University of Geneva

Why is it so transferable?

“Any new variant that qualifies to become the dominant variant is successful because it is more transmissible than its predecessor,” the epidemiologist stressed. Previously, it was the sub-variant BQ.1.1, at the origin of the 9th wave in France, which held this role, much more infectious than BA.5 (of which there are already very many).

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“So we understand that currently the variants that are positioned as candidates to dominate the epidemiological landscape are in turn highly infectious. »

If we can also sum up the three years since the start of the health crisis, the original Wuhan strain has been replaced by the Alpha variant, replaced by Delta, itself by Omicron. “Within this family, we see a somewhat similar process with BA.1, then BA.2, then BA.5, and finally BQ.1.1, which is still dominant in Europe and especially in France. »

Now a “soup of sub-variants” has taken shape, with over 650 Omicron sub-variants listed.

Antoine FlaaultEpidemiologist and Director of the Institute of Global Health at the University of Geneva

Is it more ferocious than other variants of the Omicron family?

According to the data that came to us from the United States, no new or special clinical forms have been reported. However, XBB.1.5 led to increased hospitalizations, “in proportions to which we are unfortunately now accustomed, but the frequency did not appear to be higher than that observed with the earlier variant, said Antoine Flahault. We have to stay alert, because we are at the start of this new wave there. »

How did this situation develop?

Today we have two sub-variants: XBB.1.5, which appeared in the US and looks set to arrive in Europe, and BF.7 in China.

Will XBB.1.5 win the day and in turn dominate the world stage? Will the multiple sub-variants share the epidemiological landscape? Hard to predict. For sure we are not done with this pandemic, many candidates who are more infectious than their predecessors are waiting their turn, more or less impatient, and we are dealing with a bit too many applicants right now.

Antoine FlaaultEpidemiologist and Director of the Institute of Global Health at the University of Geneva

If we haven’t finished with the variants, the professor points to the immunity afforded us by existing vaccines, which seem to continue to protect us well against serious forms. Therefore he called on residents to be vaccinated “before the tenth wave occurs”.

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