What to Know About Arcturus, the Latest COVID Variant

Health officials and virus experts are keeping a close eye on a new subvariant of omicron that’s been reported in nearly 30 countries and is growing its presence in the U.S.

Nicknamed Arcturus, and technically referred to as XBB.1.16, the strain is behind an estimated 12 percent of new COVID-19 cases in the U.S., up from 7.4 percent the previous week, data from the Centers for Disease Control and Prevention (CDC) shows. Judging by patterns seen 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 by summer.

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What this means is that we could see another surge of infections over the coming months, Binnicker says. However, he suspects this new wave will not be as bad as previous ones, like 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 some 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 first became available in September 2022, target both the original strain of the coronavirus and two omicron strains no longer in circulation. Data show the bivalent vaccines have been effective against other omicron subvariants that have emerged, and Binnicker predicts that will hold true with XBB.1.16.