A new subvariant of Omicron has emerged in the US and is already starting to accelerate quickly into poll position.
Last week the US’ Centre for Disease Control (CDC) reported that 40.5% of infections across the country were now comprised of patients with XBB.1.5, nearly doubling from 21% just one week earlier, after its emergence in traveller-based test results in September 2022.
By contrast, the original XBB strain has remained at levels around 4% across December, rising from 0.1% over the same period, while BQ.1, the other dominant strain spreading across America, has been superseded by the growth of XBB.1.5.
While XBB.1.5 originated in the US, according to an article by researchers at Columbia University, published just before Christmas in the journal Cell, XBB and XBB.1 were first identified in India in mid-August and quickly became predominant in India, Singapore, and other regions in Asia.
Lead author, Professor David Ho, explained that XBB and XBB.1 resulted from a recombination between two BA.2 lineages, BJ.1 and BA.2.75 to form one of the most immune resistant strains to date.
“Strikingly, the spike of the predominant XBB subvariant has 14 mutations in addition to those found in BA.2, including 5 in the N-terminal domain (NTD) and 9 in the receptor-binding domain (RBD), whereas XBB.1 has an additional G252V mutation,” Professor Ho said.
“The rapid rise of these subvariants and their extensive array of spike mutations are reminiscent of the appearance of the first Omicron variant last year, thus raising concerns that they may further compromise the efficacy of current COVID-19 vaccines and monoclonal antibody (mAb) therapeutics.
“We now report findings that indicate that such concerns are, sadly, justified, especially so for the XBB and XBB.1 subvariants.”
Researchers from Peking University, led by Professor Yunlong Cao, have already shown that XBB.1.5 is able to be transmitted more effectively due to its ability to bind more tightly to the ACE2 receptor, and estimates currently predict that the new strain has a 159.8% relative growth advantage compared to other strains.
The high transmissibility of XBB.1.5 has been linked to the F486P mutation, which was identified in mid-2022 by US based Bloom Laboratories as the most probable point for any changes to the virus’ ability to evade the immune system, during a comprehensive screen of spike protein nucleotides.
The subvariant was first documented in New York by the NY State Department of Health, based on data from the GISAID repository and CDC’s national SARS-CoV-2 genomic surveillance program.
For samples of SARS-CoV-2 collected between 4 -17 December 2022, 19.5% were BQ.1, 26.7% were BQ.1.1, 10.8% were XBB and 24.4% were XBB.1.5, yet by Christmas, 19.9% were BQ.1, only 22.1% were BQ.1.1, and those with XBB.1.5 had risen to 50.2%.
The latest statement on the sub lineages issued by the World Health Organization (WHO), back in October 2022, noted that based on currently available evidence, “the TAG-VE does not feel that the overall phenotype of XBB* and BQ.1* diverge sufficiently from each other, or from other Omicron lineages with additional immune escape mutations, in terms of the necessary public health response, to warrant the designation of new variants of concern and assignment of a new label.”
“Whether the increased immune escape of XBB* is sufficient to drive new infection waves appears to depend on the regional immune landscape as affected by the size and timing of previous Omicron waves, as well as the COVID-19 vaccination coverage,” the WHO said.
“This decision will be reassessed regularly. If there is any significant development that warrant a change in public health strategy, WHO will promptly alert Member States and the public.”
However, with the rapid transmission that has occurred over the holiday season in the Northern Hemisphere, it remains to be seen if 2023 will bring the designation of XBB.1.5 as the next big wave.