‘Arcturus,’ the latest COVID variant eyed by the WHO, appears to have a new symptom. Here's what you need to know

XBB.1.16, dubbed “Arcturus” by variant trackers, 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 others.

Tracking #SARSCoV2 lineage XBB.1.16* (#Arcturus) over time – Globally

Total Sequences : 2,393

Tracker: https://t.co/VaSl5Y3js3

Note: Recent Epi weeks are incomplete; Includes seqs from targeted & Airport surveillance

Updated: 04/10/23 pic.twitter.com/PkqoTU2c9o

— Raj Rajnarayanan (@RajlabN) April 10, 2023

But XBB.1.16 may not be just another run-of-the-mill Omicron. Dr. Vipin Vashishtha—a pediatrician in India and former head of the Indian Academy of Pediatrics Committee on Immunization—tweeted Thursday that pediatric cases of COVID are on the increase for the first time in six months, and that “an infantile phenotype seems emerging.”

The symptoms he’s now seeing among children:

• High fever
• Cough
• “Itchy” conjunctivitis—or pink eye—without pus, but with “sticky eyes”

The latter symptom hasn’t been seen in earlier COVID waves, he noted.

COVID cases in kids under 12 in India are increasing, The Times of India reported Monday. While they’re generally mild, doctors are warning “parents of children with obesity, asthma, and [those] suffering from other immunocompromised conditions not to ignore the symptoms,” and to seek care if necessary, the publication noted.

Experts told The Times they were also seeing a rise in hospitalizations of children due to adenovirus, which has symptoms similar to COVID and can also result in conjunctivitis. Adenovirus and COVID are impossible to distinguish from each other without testing.

There are “lots of anecdotals of pediatric conjunctivitis in India” right now, 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.

Richard Reithinger, an infectious disease epidemiologist at the nonprofit research institute RTI International, tells Fortune 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.

Conjunctivitis has previously been reported as a COVID symptom, he notes, though not often.

Researchers at Nebraska Medicine’s Truhlsen Eye Institute previously identified the virus in the eye’s tear film, a thin layer of fluid that covers the eye’s outer surface. The presence of the virus there could lead to conjunctivitis, the institute noted in a November blog post.

According to the Truhlsen Eye Institute, symptoms of conjunctivitis include:

• Tearing, or watery eyes
• Redness
• Swelling
• Pain or irritation
• Itching
• Discharge

XBB.1.16 has ‘the oomph to outcompete’ other variants

Rajnarayanan expects to see XBB.1.16 and another new Omicron spawn, XBB.1.9, gain steam over the next few weeks, “if nothing else emerges.”

XBB.1.16 and its descendents have “the oomph to outcompete” other circulating COVID variants—“as of now,” he says, noting that new variants evolve quickly. 

The XBB.1.16 family of variants “are the next big group” after Kraken variants, he notes.

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, tells Fortune.

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, also known as “Kraken,” which currently 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.

XBB.1.16 the most transmissible yet

The WHO declared XBB.1.16 a “variant under monitoring” in late March. It’s the most transmissible variant yet, Maria Van Kerkhove, COVID-19 technical lead for the WHO, said at a March 31 press conference.

Additional mutations in the virus’s spike protein, which attaches to and infects human cells, create the potential for it to infect more easily and even cause more severe disease. For this reason, and due to rising cases in the East, XBB.1.16 is considered “one to watch,” Van Kerkhove said at the time.

COVID hospitalizations and deaths have so far not risen in India, though both are referred to as “lagging indicators”—meaning that such developments, if they occur, usually happen several weeks after a rise in cases.

The variant still hasn’t been broken out in the U.S. by the CDC. On Friday, XBB.1.16 cases were still reported under XBB, which comprised just under 2% of U.S. cases. Cases must comprise at least 1% nationally before they’re reported in their own category.

But XBB.1.16 is clearly in the process of infiltrating the U.S. Nearly half of such sequences identified in the U.S. were identified via airport surveillance, Rajnarayanan notes, citing data from GISAID, an international research database that tracks changes in COVID and the flu virus.