Why Omicron’s XBB.1.5 Variant Takes Over on the East Coast

You may have come home with it after a recent trip to New England. Or maybe you got it from that friend or family member who came all the way from New York for the holidays.

The new Omicron subvariant of concern is XBB.1.5 and it has arrived in Southern California. This version of the coronavirus is more contagious and more resistant to existing immunity than any of its predecessors.

“It’s just the newest, biggest, most contagious variant,” said USC virologist Paula Cannon. “It’s amazing to me that this virus keeps finding one more trick to make itself even more infectious, even more transmissible.”

Along with a related subvariant called XBB.1, XBB.1.5 is a combination of two different versions of Omicron’s BA.2 subvariant. Both parents are particularly good at binding to the ACE2 receptor, the part of the cell that attacks the virus’s spike protein to initiate an infection, and their offspring appear to have inherited this talent.

In the last week of 2022, about 40.5% of the SARS-CoV-2 coronavirus specimens circulating in the US were of the XBB.1.5 variety, according to the Centers for Disease Control and Prevention. It is particularly common in the northeast of the country, where it first appeared in early November and now accounts for more than 72% of cases.

XBB.1.5 has so far had less of an impact in the region that includes California, Nevada, Arizona, Hawaii and the Pacific Islands, where its coronavirus market share is 9.2 percent, according to the CDC. (It is even less common in the mountain and midwestern states from Utah to Ohio, Michigan, and Minnesota.)

In Los Angeles County, as in most of the country, the BQ.1 and BQ.1.1 versions of Omicron still dominate, said Dr. Paul Simon, Chief Science Officer of the Los Angeles County Department of Public Health.

Two weeks ago, XBB.1.5 accounted for about 5 percent of the coronaviruses in the county, Simon said. But the county’s data lagged real life by about two weeks, he said, and he expects to see a jump in the prevalence of XBB.1.5 and the total number of coronavirus infections in the latest numbers for 2022.

“It’s predictable: after the holidays, there’s an increase in cases,” Simon said. “We saw that after Thanksgiving. We expect that to happen in the next few weeks.”

Although it seems repetitive to describe each new emerging subvariant in superlative terms, more transmissible than ever, now with an unprecedented ability to evade immunity – this is just evolution at work, said Dr. Tim Brewer, an infectious disease physician and professor of medicine and epidemiology at UCLA.

“The only way that a new version of the SARS-CoV-2 virus is going to displace the one that’s already there is that it has to have some competitive advantage,” Brewer said. “If it didn’t have a competitive advantage, it wouldn’t displace what’s already there.”

And when it comes to survival of the fittest, XBB.1.5 has several things going for it.

“It’s almost like a triple threat,” Cannon said. It is the most infectious subvariant to date. Dodges immunity imparted by a vaccine, booster, or previous infection more effectively than other subvariants. And so it was with the original Delta and Omicron variants, emerging in late fall, just in time to proliferate during the frequent indoor gatherings of the holiday season.

XBB.1.5 isn’t just making its mark in the United States. It is rapidly displacing other sub-variants of Omicron globally, confirmed the World Health Organization Wednesday.

“We expect new waves of infection around the world,” said infectious disease epidemiologist Dr. Maria Van Kerkhove, COVID-19 Leader of the WHO Health Emergencies Programme. “But this should not translate into new waves of death because our countermeasures continue to work.”

Early data suggest that XBB.1.5 and XBB.1 do not appear to cause more severe disease than earlier forms of the virus. There is also no indication that they respond differently than other subvariants to the drug Paxlovid, which lowers viral load when taken in the early days of the disease, Cannon said. (Like all other subvariants currently in circulation, it does not respond to treatment with monoclonal antibodies).

While the characteristics of the new strains make it more likely that fully vaccinated or previously infected people will test positive for an infection, the shots are still effective in preventing serious illness, Simon said.

Los Angeles County still has plenty of opportunity to weaken its chains of transmission. Disappointingly, few people have opted to get the new bivalent boosters, Simon said: Only a little more than a third of people 65 and older and a fifth of younger adults have rolled up their sleeves for shots aimed at Omicron along with the original version. . of the virus

“If you’re elderly, immunocompromised or pregnant, if you’re in one of those groups, it’s really important that you keep up with your boosters,” said Dr. Celine Gounder, infectious disease epidemiologist and senior fellow at the Kaiser Family Foundation.

“Yes, you personally may have had COVID. You may be a young, healthy person who has had their three shots,” he said. “But it’s still holding back the economy. It’s still having a big impact on healthcare institutions, which means the cost is being passed on to you as a consumer. … So there are reasons collectively that we should try to mitigate [this].”

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