XBB COVID variant presents a unique threat: study

While the U.S. and other countries focus on the increasing footprint of sub-subvariants of the omicron iteration of COVID-19, BQ.1 and BQ.1.1, healthcare systems here and around the world might also want to keep a wary eye on yet another sub-subvariant: XBB.

Japanese researchers say in a preprint study posted Tuesday that XBB exhibits a unique path into existence not seen before in COVID-19 variants, and this gives it more of a “profound resistance to antiviral humoral immunity induced by breakthrough infections of prior Omicron subvariants.”

Their findings (PDF) were posted on medRxiv, a website featuring studies that have not yet been peer reviewed. XBB was first identified by researchers at Peking University in Beijing in September, and one of the authors of that study said that “XBB is currently the most antibody-evasive strain tested.”

The study, unveiled Tuesday by researchers with the University of Tokyo, bolsters that assessment, stating that “to our knowledge, this is the first documented example of a SARS-CoV-2 variant increasing its fitness through recombination rather than single mutations.”

Recombination means the joining of variants that arise from two genetically distinct parental strains, creating opportunities for a virus to adapt to, and escape from, antibodies and other genetic roadblocks, be they produced by scientists or nature. Recombination presented a significant challenge in the early days of the fight against HIV/AIDS.

Kevin Kavanagh, M.D., is the president and founder of the patient advocacy organization Health Watch USA and has kept a close eye on COVID-19 throughout the pandemic. Kavanagh told Fierce Healthcare that “the most disturbing finding in the study is that this virus is a recombinant virus where two different genomes or genetic materials from viruses were recombined, as opposed to a chance mutation.”

Kavanagh pointed out that the U.S. healthcare system currently deals with the tripledemic of influenza, respiratory syncytial virus (RSV) and COVID-19. Kavanagh said how, in the summer, Texas Children’s Hospital had to deal with about 25 cases where children had been infected by RSV and COVID-19 at the same time.

“If viruses can start swapping genetic material, then the sky is the limit on the number of variants and the various characteristics which may be produced,” says Kavanagh. 

XBB is not as lethal as the delta variant, the deadliest iteration of COVID-19, but it is as lethal as BA.2.75, according to the study by Japanese researchers. The study notes that XBB first emerged in the summer in India and its neighboring countries, but health systems should not consider XBB a regional problem, and “this variant has a potential to spread worldwide in the near future.”

XBB’s presence in the U.S. is growing rapidly and now makes up 18.3% of new cases as of the week ending Dec. 24, according to the Centers for Disease Control and Prevention. That’s a sharp increase from the week before.

Variants Week ending Dec 24

University of Tokyo researchers said that “XBB acquired two sets of a pair of immune escape-associated and infectivity-enhancing substitutions by only one recombination event. Harboring the two sets of the substitution pairs would be one of the causes why XBB shows higher Re than other Omicron subvariants. Together, although XBB emerged via a unique evolutionary pathway, our data suggest that XBB also follows the same evolutionary rule with other Omicron subvariants.”

The R0, or R naught, estimates a pathogen’s contagiousness, accounting for biological features as well as behavior of individuals. Re is the same as R0, minus the assumption that everybody’s susceptible to infection.  

The study said that “although various ‘local variants’ including XBB have simultaneously and convergently emerged in late 2022, local variants showing a higher transmissibility will eventually spread to the whole world, like XBB. Therefore, continued in-depth viral genomic surveillance and real-time evaluation of the risk of newly emerging SARS-CoV-2 variants, even though considered local variants at the time of emergence, should be crucial.”

Kavanagh stressed that a virus created through recombination “can make huge leaps and bounds in changes in its characteristics in a very short period of time. The fact that this has been observed is even more concerning than this virus itself.”