It’s hard to keep up with the coronavirus, particularly the highly mutated and fast-moving omicron variant. In the latest U.S. development, a new omicron offshoot is multiplying at a rapid pace: XBB.1.5.
Although the Centers for Disease Control and Prevention (CDC) projected XBB.1.5 to be the predominant U.S. variant going into the new year, the health agency revised its estimate as of January 7. According to the latest figures, the omicron subvariant BQ1.1 makes up the majority of new cases (34 percent), followed by XBB.1.5 (28 percent) and BQ.1 (21 percent).
Still, XBB.1.5 is poised to take the top spot, growing more than tenfold since the beginning of December. Scientists have nicknamed it Kraken, after a gigantic tentacled sea monster in Scandinavian myth.
The subvariant has already taken over the Northeast, causing more than 7 out of 10 infections. Public health officials are keeping a watchful eye to see if that trend continues across the country in the weeks to come.
XBB.1.5 Appears to Be More Contagious Than Other Subvariants
“Obviously, XBB.1.5 is very, very contagious, because it seems to be outcompeting some of the other variants,” says William Schaffner, MD, an infectious disease specialist and professor of preventive medicine and health policy at the Vanderbilt University School of Medicine in Nashville, Tennessee.
As the CDC has reported, the subvariant has already driven outbreaks in part of Asia, including Singapore.
In a press briefing, Maria Van Kerkhove, PhD, an infectious disease epidemiologist and the COVID-19 technical lead for the World Health Organization (WHO), called XBB.1.5 the most transmissible subvariant detected so far. She explained that the mutations within XBB.1.5 allow the virus to adhere to human cells and replicate easily.
“We are concerned about its growth advantage, in particular in some countries in Europe and in the U.S. — in North America, particularly the Northeast part of the United States, where XBB.1.5 has rapidly replaced other circulating variants,” said Dr. Van Kerkhove.
In an interview on the Johns Hopkins website, virologist Andy Pekosz, PhD, a professor of molecular microbiology and immunology, suggested that even someone who has been infected with an earlier omicron subvariant is likely susceptible to reinfection with XBB.1.5 (although firm numbers on this are not yet available).
“This is for two reasons: The XBB.1.5 variant is more immune-evasive, and a person’s immune response naturally decreases over time following infection,” said Dr. Pekosz.
Do Rising Hospitalizations in New York State Foreshadow an Increase in COVID-19 Cases Across the U.S.?
New York State health figures indicate a recent steady rise in COVID-19 hospitalizations. The number of COVID-19 hospital admissions statewide stood at 3,866, the highest it has been since February of last year. Several Southern states, including Kentucky and South Carolina, are also experiencing worsening conditions.
“We don’t know for sure how much of this [specifically New York hospitalizations] is being driven by XBB.1.5, but it doesn’t look favorable,” wrote Eric Topol, MD, president of Scripps Research, in his online publication Ground Truths. “It is at the very least contributing — too much of a coincidence to see such a striking rise of the variant along with New York’s data.”
On January 11, however, the WHO presented a risk assessment of XBB.1.5, finding that the subvariant does not have any mutations known to make people sicker.
Do COVID-19 Vaccines Protect Against XBB.1.5?
Because XBB.1.5 is part of the omicron family, Dr. Schaffner believes that current vaccines will offer substantial protection against a mild or moderate infection developing into severe illness.
“I think from the vaccine point of view, we’re still okay,” says Schaffner. “So in that sense, [XBB.1.5] is not yet a variant of concern, but it does continue to be a variant of great interest, simply because it seems to be running the table, so to speak.”
Schaffner encourages everyone to get up-to-date with their COVID-19 vaccines, including the new bivalent booster shots. “They may not protect against mild infections but they certainly protect against severe disease,” he says.
According to the latest CDC data, only 15 percent of eligible Americans have received the most recent booster.
The WHO noted (PDF) on January 11 that “there is currently no data on real world vaccine effectiveness against severe disease or death” when it comes to XBB.1.5.
