As multiple respiratory viruses circulate in the United States, a subvariant of Omicron named XBB.1.5 appears to be poised to dominate other strains of the virus. Estimates from the Centers for Disease Control and Prevention (CDC), find that XBB.1.5 has risen from about 4 percent to 41 percent of new COVID-19 infections over the month of December. The CDC estimates that it’s causing 75 percent of new cases in the northeastern US.
[Related: Omicron boosters are the future of COVID vaccines in the US.]
“For a few months now, we haven’t seen a variant that’s taken off at that speed,” Pavitra Roychoudhury, director of COVIC-19 sequencing at the University of Washington School of Medicine’s virology lab, told CNN.
It is not yet clear where this version of Omicron came from, but it may have arisen in the United States. In late October 2022, it was first detected in Connecticut and New York, according to GISAID, an international effort to catalog and track COVID-19 variants.
XBB.1.5 was created by recombination that occurred when two descendants of Omicron’s BA.2 subvariant swapped pieces of their genetic code. The result was 14 new mutations to the virus’ spike proteins compared with BA.2 and a new sublineage named XBB.
XBB drove a wave of COVID-19 cases in Singapore during the fall of 2022. In the US, XBB faced competition from co-circulating variants that have each evolved some of the same mutations. According to the World Health Organization (WHO), XBB has been found in at least 70 countries.
[Related: Omicron variants keep getting better at dodging our immune systems.]
One of XBB.1.5’s main differences from the earlier XBB variant is that it can attach itself to cells more efficiently. “The virus needs to bind tightly to cells to be more efficient at getting in and that could help the virus be a little bit more efficient at infecting people,” Andrew Pekosz, a virologist at Johns Hopkins University, told CNBC.
Another concern surrounding this new strain is waning immunity. Vaccination or previous COVID-19 infection appear to only prevent reinfection for a few months in some cases, and the virus’ evolution adds an additional immunity challenge. There has also been limited uptake of the bivalent booster, that is targeted to fight both the original strain of COVID-19 and Omicron. Only 17 percent of adults have received this updated booster, despite evidence showing that it increases protection against severe illness and death.
While it is not completely clear if XBB.1.5 causes a more severe form of the illness or will increase hospitalizations, data shows that hospitalizations in the US are about to surpass the number seen during a spike of the virus in summer 2022. Multiple factors from this continued evolution of the virus and holiday gatherings appear to be driving transmission and the increase is a sign that an anticipated winter COVID-19 wave has begun.
The best ways to prevent infection include wearing a high-quality mask, especially in crowded indoor settings, regularly testing for COVID-19, and staying up to date on vaccinations.