‘Arcturus,’ a COVID variant sweeping India, is now in the U.S., the CDC says—and it’s coming in hot. What it means for the future of the pandemic

And it’s coming in hot. XBB.1.16, dubbed “Arcturus” by variant trackers, is estimated to be behind 7% of COVID cases in the country this week, according to the CDC’s Nowcast, a viral forecast released each Friday by the national public health agency. The variant doesn’t look to cause more severe disease, according to a COVID situation report released Thursday by the World Health Organization.

#SARSCoV2 #VariantProportions – #USA |04/14/23

New @CDCgov #Nowcast estimates:

>> XBB.1.16, XBB.1.9.2 and FD.2 make an entry! <<

Top circulating lineages:
XBB.1.5 (78%)
XBB.1.16 (7.2%)
XBB.1.9.1 (6.5%)
XBB.1.9.2 (2.5%)
—
FD.2 (1.7%)https://t.co/ZWTuG25j4T
1/n pic.twitter.com/AjAusZVYS2

— Raj Rajnarayanan (@RajlabN) April 14, 2023

Friday was the first time the CDC had assigned XBB.1.16 its own category. Before then, cases had been lumped under XBB.

XBB variants hold the top six spots in the U.S. when it comes to variant frequency. XBB.1.5, also known as “Kraken,” rose to U.S. prominence during a winter wave of cases. It’s still thought to represent more than three-quarters of U.S. cases, though levels are waning.

XBB.1.9.1, XBB.1.9.2, and XBB.1.5.1 hold the third, fourth, and fifth spots, respectively, each comprising between 2.4% and 6.5% of cases.

FD.2—a shortened name for another XBB spawn, XBB.1.5.15—comes in at No. 6, and is estimated to fuel nearly 2% of U.S. cases this week.

While XBB.1.5 is still technically “top dog” in the U.S., it “looks spent,” Raj Rajnarayanan, assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., and a top COVID variant tracker, tells Fortune.

While XBB.1.16 looks to be on the path for eventual U.S. dominance, other up-and-coming Omicron spawn could provide competition, Rajnarayanan says, like XBB.2.3 and descendants, and XBC.1.6 and descendants.

Rising cases in India, with a possible new symptom

XBB.1.16 is fueling a new surge of cases in India, at a time when reported cases are down in much of the rest of the world. The country’s health ministry is holding mock drills to ensure that hospitals are prepared for rising COVID cases, the BBC reported Monday, noting that some states have again made mask-wearing in public mandatory.

Levels of the variant are also rising in the U.S., Singapore, and Australia, among other countries.

Reports from India indicate that the variant’s symptom set may be changing—at least slightly, and at least in children. Reports of conjunctivitis, or pinkeye, without pus, but causing “sticky eye” are on the rise among children in the country. It’s a symptom that hasn’t often been noted with other COVID variants, Dr. Vipin Vashishtha—a pediatrician in India and former head of the Indian Academy of Pediatrics Committee on Immunization—tweeted last week.

There are “lots of anecdotals of pediatric conjunctivitis in India” right now, Rajnarayanan, previously told Fortune.

Richard Reithinger, an infectious disease epidemiologist at the nonprofit research institute RTI International, told Fortune earlier this week that he’s also heard such reports, but that it’s “probably too early to tell” if the virus’s symptom set has truly shifted.

Cases of adenovirus in children are also reportedly on the rise in India. Adenovirus can also cause conjunctivitis—and it’s impossible to distinguish the two viruses from each other without testing.

Pandemic now in an ‘age of recombinants’

When it comes to the pandemic, the world is currently in the “age of recombinants”—or existing variants that have combined with each other to potentially wreak more havoc—Ryan Gregory, a biology professor at the University of Guelph in Ontario, Canada, told Fortune earlier this week.

XBB.1.16 is a recombinant of two descendants of so-called “stealth Omicron” BA.2. A preprint study updated Sunday from scientists at the University of Tokyo suggests that it spreads about 1.17 to 1.27 times more efficiently than relatives XBB.1 and XBB.1.5, which still dominates U.S. cases.

XBB.1.16’s increased ability to outpace other variants suggest that it “will spread worldwide in the near future,” researchers wrote, adding that the variant is “robustly resistant” to antibodies from a variety of COVID variants, including “stealth Omicron” BA.2 and BA.5, which surged globally last summer.

That means it could cause cases to rise again, even in areas that have recently seen increased COVID infections—especially if those infections stemmed from either BA.2, BA.5, or their descendants.

New variants may not always cause “waves” of cases anymore. That’s because a continual parade of new Omicron variants creates a baseline of infections that remains “unsustainably high,” Gregory says.

This is a developing story and will be updated.