After China, attention turns to the situation across the Atlantic. In the viewfinder: the new sub-variant of Omicron XBB.1.5 which is spreading in the United States at great speed. “XBB.1.5 is more worrying than BF.7, which is circulating in China, because the latter is not not subject to the same immune pressure,” says Sandie Munier, lecturer at Paris Cité University and member of the French Society of Virology. On Wednesday, January 4, US experts expressed concern over the rapid growth of the new Omicron subline. During the month of December, the percentage of new infections linked to XBB.1.5 in the United States increased from approximately 4% to 41%. “This is an amazing increase,” Dr. Ashish Jha, the White House’s Covid-19 response coordinator, wrote on Twitter.
In some areas of the northern United States, such as New York State, this new strain has become the majority – it accounts for nearly 70% of cases. “The variant is likely to become dominant in the country within a week,” says the European Center for Disease Prevention and Control (ECDC), in a report published Thursday, January 5. By way of explanation, the health agency believes that the subvariant has a “growth advantage” over lines previously circulating in North America (139%) and Europe (137%), although these estimates are associated with “large uncertainty”.
How to explain this strong contagiousness? “XBB 1.5 comes from XBB, which is a recombinant of two variants. It has a mutation, S486P, which gives it a transmission advantage”, answers Hervé Fleury, virologist and professor emeritus at the CNRS and the University of Bordeaux. Thanks to this mutation, the virus clings more effectively to ACE2 receptors, which makes it more transmissible. “We do not know the impact this may have on long Covid, because XBB.1.5 could infect a wider variety of cells”, supports Sandie Munier.
This growth advantage could also be explained by its ability to resist immunity more than the previous variants, whether due to vaccination or infections. Further investigations are needed to elucidate this mechanism. This sub-variant of Omicron is still young and some of its specific characteristics are still unknown, whether in terms of transmissibility or escape from immunity. “We hope, for example, that it responds well to antivirals such as Paxlovid prescribed for the most vulnerable, but here too we still lack perspective”, admits Antoine Flahault, director of the Institute of Global Health and professor at the faculty. of Medicine in Geneva.
Low circulation of XBB.1.5 in France
In France, the sub-variant circulates “at fairly low levels” and does not currently arouse “particular concern”, underlined, Friday January 6, the French public health agency in its weekly update. “Between 30 and 50 sequences of this variant have been identified in recent weeks,” said Justine Schaeffer, variant expert. So far, it has spread to at least 29 countries, according to World Health Organization figures as of January 5. And could be the engine of a resumption of the epidemic in Europe, “but not in the coming month, because it is present in the EU only at very low levels”, specifies the ECDC.
This does not prevent the feeling of concern among certain European politicians. “Let’s hope we get through the winter before such a variant can spread among us,” German Health Minister Karl Lauterbach wrote on Twitter on Wednesday evening. The transposition of the American curve to Europe remains uncertain, as there are major differences between the two countries. “Vaccination coverage is more homogeneous in Europe and France than in the United States. Antivax and anti-science movements have proliferated more across the Atlantic, especially in Republican States”, explains Antoine Flahault. Also, the Old Continent has been crossed by successive waves and France could benefit from the release of a ninth wave carried by the BQ.1.1 variant.
If XBB.1.5 is more transmissible, there are no signs of increased severity. “There are currently insufficient data available to assess any change in the severity of infection associated with this variant,” the ECDC said. The question of virulence is always more difficult to decide. “The more time passes, the more the immunological histories of individuals become richer, and it becomes very difficult to measure the virulence of a strain, because the expression of the severity of the disease depends on the intrinsic virulence of the pathogen but also on the immunity of the individual”, explains Mircea Sofonea, epidemiologist at the University of Montpellier.
“Sars-CoV-2 has not finished evolving”
Same story on the side of Sandie Munier: “We are seeing an increase in hospitalizations linked to Covid-19 in the United States, but it is still too early to draw hasty conclusions on greater pathogenicity.” This increase in hospitalizations and deaths seems mainly linked to the increase in cases, and in proportion to the serious forms. Again, there is not enough information available at this time. Because it takes several months to properly characterize a strain. “Virologists can, on the basis of the knowledge on the mutations of the virus that we first have, make first hypotheses on its pathogenicity, its transmission and its possible immune escape. But these are only preliminary hypotheses that should be considered. to then validate on clinical data. Currently, we are in this validation phase which always takes several weeks”, underlines Antoine Flahault.
Patience, therefore, before the contours of XBB.1.5 become clearer. Good news, though: the circulation of the subvariant should be easier to monitor. “In XBB.1.5, there is no L452R mutation, unlike the BA5 and BA4 sub-lineages which were the majority. We will therefore be able to recover information again from the screening”, resumes Mircea Sofonea. If the scientists remain in expectation concerning this newcomer, the interest around this sub-variant is strong. “It highlights the genetic capacity of Sars-CoV-2: when Alpha arrived, then Beta and Gamma, we were told that there was a finite reservoir of evolutionary potential. Same with Omicron. However, the evolution continues to occur at a sustained pace with several waves per year. Sars-CoV-2 has not finished evolving”, concludes the specialist.