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What to Know About Arcturus, the Latest COVID Variant

Experts say the strain, formally known as XBB.1.16, could cause a summer surge

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Eugene Mymrin / Getty Images

Health officials and virus experts are keeping a close eye on a new subvariant of omicron that’s been reported in many countries and has a growing presence in the U.S. 

Nicknamed Arcturus, and technically referred to as XBB.1.16, the strain is behind an estimated 18.2 percent of new COVID-19 cases in the U.S., up from 7.4 percent in late April, data from the Centers for Disease Control and Prevention (CDC) shows. Judging by patterns in other countries — especially India, where XBB.1.16 is more widespread — Matthew Binnicker, director of the clinical virology laboratory at Mayo Clinic, predicts the subvariant will outpace the current dominant strain in circulation (XBB.1.5) and take the lead this summer. Currently, XBB.1.5 accounts for about 40 percent of COVID-19 cases in the U.S. 

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What this means is we could see another surge of infections over the coming months, Binnicker says; however, he suspects this new wave would not be as bad as previous ones, such as when omicron and delta first burst onto the scene.  

A big reason: “There is a high level of existing immunity in the population, either [from] prior infection or from vaccination,” Binnicker says. This immunity reduces the risk of reinfection, or severe illness if a person is infected, though the CDC notes that protection does wane over time. 

More recently, health officials gave the all-clear for adults 65 and older and immunocompromised individuals to get a second bivalent booster to restore diminished protection. These updated vaccines, which became available in September 2022, target the original strain of the coronavirus and two omicron strains (BA.4 and BA.5) no longer in circulation. Data shows the bivalent vaccines have been effective against other omicron subvariants that have emerged, and Binnicker predicts that will hold true with XBB.1.16.

An XBB-specific vaccine could be available in the fall. On June 15, an advisory committee to the U.S. Food and Drug Administration (FDA) voted unanimously in favor of updating the shots to take aim at the XBB lineage. If the FDA agrees, the new vaccines could be ready sometime in September. 

Does the new subvariant cause new symptoms?

So far, there’s no sign that this subvariant causes people to get sicker, officials with the World Health Organization (WHO) say. In the U.S., hospitalizations and deaths from COVID-19 have steadily declined since winter, federal data shows, though they remain highest among the older adult population. 


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However, symptoms may differ with XBB.1.16. Conjunctivitis, or pink eye, has been linked with COVID-19 in the past, but Binnicker says some doctors in India have noted it’s popping up more often in people infected with XBB.1.16, especially in children. Some people may also experience higher fevers, he says. 

“So those are two things for physicians to keep an eye on as we start to see an increase in prevalence here in the U.S.,” Binnicker says. 

This time of year, the red, itchy eyes that accompany conjunctivitis could easily be blamed on seasonal allergies. Conjunctivitis can also be a symptom of other viral infections, such as adenovirus, which is spiking in the U.S., national surveillance data shows. Binnicker says this underscores the importance of getting tested for the coronavirus if you experience any symptoms related to an infection. With a positive test, you could be eligible for antiviral treatments that can significantly reduce your risk of severe COVID-19 complications.

Video: What You Should Know About the New COVID Variant ‘Arcturus’

Another tip: Stay vigilant. WHO Director Tedros Adhanom Ghebreyesus said in a media briefing that the emergence of XBB.1.16 illustrates that the “virus is still changing and is still capable of causing new waves of disease and death.” 

Editor's note: This story, originally published May 1, 2023, has been updated to reflect new information.

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