A highly contagious new subvariant of the COVID-19 virus that’s fueling rising case numbers in the northeastern United States has been detected in Arizona, but unlike some other parts of the country it’s not yet dominant here.
Arizona historically has been hit with surges of COVID-19 later than most other states and the level of the XBB.1.5 subvariant that’s been detected here so far is extremely low. While its levels could rise in the coming weeks, that’s not inevitable, said David Engelthaler, who leads the infectious-disease division of the Arizona-based Translational Genomics Research Institute.
“Although we’ve been seeing it (XBB.1.5) here in Arizona since early December, it hasn’t taken off yet. It’s not one of our dominant strains. Here, it’s one of dozens of subvariants we seem to have in Arizona right now,” Engelthaler said. “The best we can do in my mind is work with the most vulnerable, those that are over 70 years of age, make sure their immunity is boosted, whether it’s from a recent infection or a recent booster shot. That’s just going to continue to prevent them from getting a serious outcome.”
It’s not clear whether XBB.1.5 causes more severe illness than other variants of COVID-19 and it’s also not a given that it will cause a surge of cases in Arizona, some experts say, noting that XBB.1.5 took off on the East Coast during cold winter temperatures and a holiday season when people were more likely to be gathering in large groups indoors.
Arizona’s warmer weather may prove to be advantageous against high levels of XBB.1.5 transmission.
“Right now, we are relying on data and the data isn’t great. We are flying blind a little bit. We don’t have great testing data anymore, especially with a lot of home testing and most of that doesn’t get reported,” Engelthaler said. “We can still watch the trends, and that’s important to do. … It definitely should not be considered a panic moment but what is important is that we continue to keep watching this closely.”
‘The most transmissible subvariant that has been detected yet’
XBB.1.5 is “not a game changer” to Efrem Lim, an Arizona State University virologist. It’s still part of the omicron family of variants, so it’s not a new variant. ASU scientists as of Wednesday had identified 12 cases of XBB.1.5 in the positive COVID-19 tests they’ve sequenced.
“XBB.1.5 sounds different, but it is a recombinant of two omicron sublineages. So it’s still omicron,” Lim said.
Omicron and its descendants have a preference for upper respiratory cells and doesn’t tend to cause deep lung pneumonia and severe, systemic infections, Engelthaler said.
Also, it’s helpful that the updated COVID-19 bivalent booster vaccine is tailored omicron. While XBB.1.5 is derived from the BA.2 subvariant of omicron and XBB.1.5 is derived from BA.5, the updated booster shot has been shown to generate antibodies that recognize BA.2, Andy Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health, said in a Jan. 6 interview published on the school’s website.
XBB.1.5 is more of a threat to people who are unvaccinated, University of Arizona virologist Felicia Goodrum said.
“In the vaccinated population, there is little to worry about − the vaccine is holding strong in protecting against severe disease and hospitalization and is just as effective against this variant,” Goodrum wrote in an email. “Vaccinated people may still get infected and have mild illness. The threat is to unvaccinated people, the elderly who do not mount sufficient immunity even to a vaccine and people who are immunocompromised. This is the same for all variants.”
There is no reason not to expect that XBB.1.5 will dominate in Arizona, Goodrum wrote.
“All variants have arrived here later than the NE and NW areas of the countries. It should take no more than a few weeks as people travel in and out,” she wrote. “XBB.1.5 is highly transmissible so that can pose a problem for hospitals in that they will feel the strain of more cases.”
The good news is that an unusually early and severe flu and respiratory syncytial virus season in Arizona appears to be waning, which could remove some stress from the health care system in the event that there is a rise in severe COVID-19 illness, though many hospitals continue to struggle with staffing shortages.
The not-so-good news is that XBB.1.5 is really contagious, or as University of Southern California virologist Paula Cannon recently told USA Today, it’s “crazy infectious.” World Health Organization officials on Jan. 4 said XBB.1.5 had been detected in 29 countries and is “the most transmissible subvariant that has been detected yet.”
XBB.1.5 as of the week ending Jan. 7 was estimated to comprise more than 70% of reported cases in northeastern regions of the country that include New York, New Jersey, Connecticut and Massachusetts, according to model-based projections from the Centers for Disease Control and Prevention.
XBB.1.5, which has also been nicknamed the kraken variant, made up nearly 28% of all COVID-19 cases in the U.S. as of the week ending Jan. 7, according to CDC estimates, though Lim said the CDC estimates are not always the same as what’s actually happening on the ground as positive cases are sequenced.
“Is it going to be as prevalent in a few weeks?” Lim said. “We can’t say that there is going to be a surge coming just because of XBB.1.5. Now, as people have been traveling for the holidays, could that result in more cases in two or three weeks? It’s possible … but I wouldn’t say it’s necessarily going to be driven by XBB.1.5.”
Here are five things to know about XBB.1.5:
People who have been vaccinated or previously infected are still vulnerable to infection from XBB.1.5
XBB.1.5 appears to evade antibodies from vaccination and from prior infection. It has a mutation called F486 that easily invades and binds to human cells, allowing the virus to replicate and transmit more efficiently than prior descendants of the omicron variant.
“We now have all this population level of immunity from prior exposure,” Engelthaler said. “It doesn’t prevent us from getting infection because it (XBB.1.5) doesn’t really care too much about our antibody loads.”
At least five in six American adults likely have some level of immunity to COVID-19, either through vaccination or previous infection, according to a December report from the COVID States Project, a multi-university project comprising researchers from Harvard University, Northeastern University, Northwestern University, and Rutgers University. The researchers found that individuals vaccinated against COVID-19 report being sick for fewer days than unvaccinated people.
“It still seems to readily cause infection, but those infections are typically mild − very much upper respiratory, in many cases just mild cold-like symptoms or scratchy throat,” Engelthaler said. “But it is not causing anything more serious, causing anything in the lower lungs.”
The fact that XBB.1.5 can evade immunity and has an increased ability to infect cells is to be expected as a virus mutates over time, Lim said.
“When we have many more mutations occurring as a totally new variant − those are the kind of variants that could lead to a new surge.”
It’s unclear whether XBB.1.5 causes more severe illness than other COVID-19 variants, but it may still cause Long COVID
“The data is not really good yet, especially with these new subvariants, the milder illness, how much of that actually results in Long COVID,” Engelthaler said. “It is being studied closely but that is a possibility. It’s also a possibility with a lot of our other viral illnesses. It’s not a COVID-only phenomenon. We’re just learning more about the long-term effects of viral infections.
Lim said the threat of Long COVID is a key reason why people need to continue staying home when they are sick and take other precautionary steps like wearing masks in indoor public areas when community transmission levels are high. Long COVID can happen after an individual’s first case of COVID-19, but also after a reinfection, he said.
“We still don’t have a really good way to treat Long COVID,” Lim said.
Older people and people with compromised immune systems are most at risk
Older people have a more difficult time maintaining immunity to COVID-19, which makes them more vulnerable. And people of all ages with weakened immune systems are at risk of serious illness from XBB.1.5 or any COVID-19 variant.
The antiviral Paxlovid appears to work against XBB.1.5
There’s nothing about XBB.1.5 that would make it resistant to the antiviral COVID-19 treatment Paxlovid, Lim said.
Dr. Ashish Jha, White House COVID-19 response coordinator, tweeted Jan. 4 that both Paxlovid and the oral pills Molnupiravir “should work fine” against XBB.1.5 “based on what we know.” Jha later tweeted that anyone who is infected and is at elevated risk of serious illness from COVID-19 should take Paxlovid, even if their symptoms are mild.
“Anyone over 50 with a chronic disease should consider getting Pax,” he tweeted.
The updated COVID-19 booster shot should help but most Arizonans haven’t received it
“The most important thing the public needs to know is that the vaccines are the best defense to protecting themselves and others,” the UA’s Goodrum wrote. “Two doses of any of the mRNA vaccines plus at least one booster will provide very strong protection against severe disease. “
If people are high risk or care for people that are, they should consider using a high quality mask (KN95 or better) in public places with lots of people, Goodrum wrote.
“Masking, distancing and hand washing are really effective ways to limit transmission in addition to vaccination. Combining a few of these measures with vaccination is really very protective.”
Even though public health officials recommend the updated bivalent COVID-19 booster vaccine, just 14% of the Arizona population over the age of five had received it as of Jan. 4, CDC data shows.
Reach health care reporter Stephanie Innes at Stephanie.Innes@gannett.com or at 602-444-8369. Follow her on Twitter @stephanieinnes.
