XBB.1.5 Coronavirus Subvariant Spreads Quickly In U.S.

ACROSS AMERICA — The new coronavirus subvariant XBB.1.5 — one global health officials call the “most transmissible” descendant yet of the omicron variant — could fuel new cases of COVID-19.

In the United States, XBB was responsible for more than 27 percent of cases last week, up from about 2 percent the first week of December, according to the Centers for Disease Control and Prevention.

In the Northeast, more than 70 percent of cases are believed to be XBB, according to the CDC COVID-19 tracker. In other regions, the strain is estimated at less than a third of new infections.

“That’s a stunning increase,” White House COVID-19 response coordinator Dr. Ashish K. Jha tweeted last week of the rapid rise in XBB cases, at the same time telling Americans it’s “critical” that Americans are up-to-date on bivalent booster shots.

Only about 15 percent of eligible Americans have gotten their bivalent booster shots. That includes 38 percent of older Americans, who are most at risk of a serious illness.

“For folks without a very recent infection or a bivalent vaccine, you likely have very little protection against infection. And for older folks, diminishing protection against serious illness,” Jha tweeted.

XBB.1.5 combines traits of previous mutations, which health experts say make it spread more easily, even among previously infected or vaccinated people.

It’s more transmissible because of the mutations it has that allow the “virus to adhere to the cell and replicate easily,” Dr. Maria Van Kerkhove, technical lead on COVID-19 for the World Health Organization, told reporters last week.

“The more this virus circulates, the more opportunities it will have to change,”

There is no evidence XBB is more severe than other omicron strains, Van Kerkhove said.

“We are concerned about its growth advantage, in particular in some countries,” Van Kerkhove said, singling out Europe and the Northeast U.S., “where XBB.1.5 has rapidly replaced other circulating variants.”

COVID-19 infections have declined over the past year, to 470,699 weekly cases on Jan. 4, down from last year’s high of more than 5.6 million cases a week on Jan. 19, 2022.

Jha said he’s concerned about XBB, but “Am I worried this represents some huge set back?” he said. “No.”

Besides getting a bivalent vaccine, Jha said Americans should take COVID-19 tests before large gatherings or if they will be seeing someone who is vulnerable. Also, he said, wear high-quality facemasks in crowded indoor spaces, and “work to improve ventilation/filtration in indoor spaces.”

Anyone showing symptoms should get tested right away. The Paxlovid Molnupiravir treatments “should work fine based on what we know,” he said.