A new COVID variant, marking a fusion between two recent strains that is even more contagious than its predecessors, has taken hold here in New England. But what exactly is it, how serious is it and what are the symptoms?
Here's a look at what we know so far and what experts are saying:
What Is XBB.1.5?
The variant is XBB.1.5, a highly contagious "recombinant" variant that spawned from two different BA.2 variants. It is related to the XBB variant, which was previously behind a COVID surge in Singapore.
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Where is XBB.1.5 Highest Right Now?
Within the last two months, tracking numbers from the Centers for Disease Control and Prevention showed the XBB.1.5 variant has climbed to now make up more than 40% of cases in the U.S. But here in New England, XBB.1.5 accounts for a whopping 75% of all COVID-19 cases. Only three weeks ago, XBB.1.5 accounted for only 11% of COVID cases in the region.
"I never like when I see anything make a dramatic jump like we have seen with XBB," Tufts Medical Center's Dr. Shira Doron told NBC10 Boston this week. "This ascent is sharp and striking."
Is XBB.1.5 Making People Sicker?
The rapid rise in dominance has led some experts to question whether or not the variant will lead to added concerns in the weeks following holiday gatherings, with COVID hospitalizations already rising in the U.S.
Experts say the variant is clearly more infectious than other variants, meaning it's spreading more easily and outcompeting the other variants.
Andrew Pekosz, a virologist at Johns Hopkins University, told CNBC the XBB.1.5 has an additional mutation that makes it bind better to cells.
"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," Pekosz said.
While it's not clear where the variant originated exactly, so far it has not shown signs of leading to more severe infections.
"It does remind me of a year ago when omicron came in over a two-to-four week period and displaced everything," Boston Medical Center's Dr. David Hamer said. "This is sort of going that direction, but I think we need more data. Over the next two-to-four weeks we'll see what happens."
One concern is that recent strains of COVID have left some treatment options ineffective. For example, the virus has mutated enough that the XBB.1.5 subvariant is immune to monocolonal antibody treatments that had proven effective against earlier strains.
Still, experts say XBB remains an omicron subvariant, which offers less risk than if the variant were in an entirely different family.
Do Boosters Work on XBB.1.5?
Experts have said the bivalent COVID booster appears to offer some protection against the newer strains, particularly against severe illness, in large part because they remain under the omicron family.
"It does look like the vaccine, the bivalent booster is providing continued protection against hospitalization with these variants," Pekosz told CNBC. "It really emphasizes the need to get a booster particularly into vulnerable populations to provide continued protection from severe disease with these new variants."
What Are the Symptoms Associated With the Variant?
COVID symptoms haven't really changed with the new variant, though it does appear that symptoms similar to the flu are less common, particularly in those who are vaccinated and boosted.
Typical symptoms include:
- Sore throat
- Hoarse voice
- Nasal congestion
- Runny nose
- Muscle aches
Unlike earlier variants like delta that affected the lungs, omicron and its subvariants tend to cause more upper respiratory symptoms, doctors say.