A new subvariant of COVID-19 is increasing in the US and is now responsible for nearly 10% of all new cases, according to alerts from the Centers for Disease Control and Prevention and World Health Organization.

The CDC estimates that omicron strain XBB.1.16 — more commonly known as “Arcturus” — was the cause of 9.6% of new infections this week. That represents an increase from nearly 6% last week and about 3% the week prior.

Because of the spike in infections, the World Health Organization is warning the public of the possibility that the new strain could become the dominant strain in the US in the near future.

“Due to its estimated growth advantage and immune escape characteristics, XBB.1.16 may spread globally and contribute to an increase in case incidence,” WHO announced in a new report. “However, at present, there is no early signal of an increase in severity.”

WHO has now upgraded Arcturus to a “variant of interest.”

The Arcturus strain — one of more than 600 Omicron subvariants — was first detected in January and since then has been discovered in 31 countries.

It was reported earlier this month that Arcturus was causing special concern in India, and that it could be 1.2 times more infectious than the Kraken variant.

Arcturus has surpassed the other variants in India, causing India’s health ministry to launch mock drills in order to see if hospitals are properly prepared to handle a potential influx of COVID patients.

“It’s been in circulation for a few months. We haven’t seen a change in severity in individuals or in populations, but that’s why we have these systems in place,” Dr. Maria Van Kerkhove, the World Health Organization’s COVID-19 technical lead, said during a press conference.

“Systems to track the virus variants, global collaborations to assess transmissibility, immune escape, severity and the impact of any of our interventions including diagnostics, therapeutics and vaccines.”

“Dr. Van Kerkhove added, “It has one additional mutation in the spike protein which in lab studies shows increased infectivity as well as potential increased pathogenicity.”

A study from the University of Tokyo published on the biology research website bioRxiv suggested that Arcturus is 1.2 times more infectious than the Kraken variant, writing that it will “spread worldwide in the near future.”

Mutations of the new variant could potentially make it more difficult for the immune system to take on, increasing the growth rate, scientists suggested.