Why the XBB.1.5 variant of Omicron is taking over on the East Coast

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

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

“It’s just the newest and best and most contagious variety,” said Paula Cannon, a virologist at USC. “I find it amazing that this virus keeps finding a trick to make itself even more contagious, 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 attaching to the ACE2 receptor – the part of the cell that the virus attacks to start an infection – and their offspring appear to have inherited this talent.

As of the last week of 2022, about 40.5% of SARS-CoV-2 coronavirus samples circulating in the United States were of the XBB.1.5 strain, according to the Centers for Disease Control and Prevention. It is particularly prevalent in the northeast of the country, where it first emerged in early November and now accounts for more than 72% of cases.

XBB.1.5 has so far had less impact on the region, which includes California, Nevada, Arizona, Hawaii and the Pacific Islands, where the CDC says the coronavirus market share is 9.2%. (It’s even less common in the mountainous and Midwestern states from Utah to Ohio, Michigan, and Minnesota.)

In Los Angeles County, as in most parts of the country, Omicron’s BQ.1 and BQ.1.1 versions 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% of the county’s coronaviruses, Simon said. But the county’s data lags real-life by about two weeks, he said, and he expects an increase in the prevalence of XBB.1.5 — and the total number of coronavirus infections — in the latest figures of 2022.

“It’s predictable: after the holidays, there’s a spike in cases,” Simon said. “We saw it after Thanksgiving. We assume that this will be the case in the next few weeks.”

While it may sound like a repetitive use of superlatives to describe each emerging new subvariant – More transferrable than ever, now with unprecedented ability to bypass immunity – that’s just evolution at work, said Dr. Tim Brewer, an infectious disease physician and professor of medicine and epidemiology at UCLA.

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

And when it comes to survival of the fittest, XBB.1.5 has a lot to offer.

“It’s almost like a triple threat,” Cannon said. It is the most contagious sub-variant to date. It evades immunity conferred by a vaccine, booster shot, or previous infection more effectively than other subvariants. And as was the case with the Delta and original Omicron variants, they popped up in late fall – just in time to proliferate during the frequent indoor gatherings of the holiday season.

XBB.1.5 isn’t just making a name for itself in the United States. It is rapidly displacing other Omicron subvariants worldwide, confirmed the World Health Organization Wednesday.

“We expect further waves of infection around the world,” said Dr. Maria Van Kerkhove, infectious disease epidemiologist, COVID-19 director for the WHO Health Emergencies Programme. “But that doesn’t have to lead to more death waves because our countermeasures continue to work.”

Early data suggests that XBB.1.5 and XBB.1 do not appear to cause more severe disease than previous forms of the virus. There’s also no evidence that they respond differently than other subvariants to the viral load-reducing drug Paxlovid when taken in the earliest days of the disease, Cannon said. (Like all other subvariants currently circulating, it is not responsive to monoclonal antibody treatment.)

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 vaccinations are still effective in preventing serious diseases, Simon said.

Los Angeles County still has many ways to weaken its transmission chains. Disappointingly few people have taken up the new bivalent boosters, Simon said – just over a third of people aged 65 and over and a fifth of younger adults have rolled up their sleeves to take a shot at Omicron alongside the original version of the virus.

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

“Yes, you personally may have moved on from COVID. Maybe you’re a young, healthy person who got her three shots,” she said. “But that’s still holding the economy back. It still has a major impact on healthcare facilities, which means the cost is passed on to you, the consumer. … So there are reasons overall that we should try to mitigate [this].”

https://www.latimes.com/science/story/2023-01-05/xbb-1-5-variant-is-taking-over-the-east-coast-will-it-happen-in-california Why the XBB.1.5 variant of Omicron is taking over on the East Coast

Alley Einstein

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