A new Omicron subvariant on the radar of the World Health Organization—one some experts say could be the most immune-evasive yet—has been identified in the U.S., the Centers for Disease Control and Prevention told Fortune on Thursday.

There have been two cases of BA.2.75, dubbed “Centaurus,” detected in the U.S., with the first being identified on June 14, a spokesperson for the CDC said.

The CDC does not publicly report on emerging variants until they comprise 1% of cases. Thus, current cases of BA.2.75 are being reported on the agency’s data tracker under BA.2 cases, which comprised less than 3% of reported U.S. cases last week, according to data released on Tuesday.

Centaurus has recently risen to prominence in India, competing with the BA.5 Omicron subvariant that is sweeping the globe. WHO officials said they were tracking the ultra-new subvariant at a Wednesday press conference and released some information about it via Twitter on Tuesday.

https://twitter.com/WHO/status/1544413181027778561

BA.2.75 has been reported in “about 10 other countries” and has not been declared a variant of concern, Dr. Soumya Swaminathan, WHO's chief scientist, said in a Tuesday tweet. Transmissibility, severity, and potential for immune evasion are currently unknown, she added.

But some experts are raising potential red flags. Dr. Eric Topol, a professor of molecular medicine at Scripps Research and founder and director of the Scripps Research Translational Institute, said Monday the new subvariant’s mutations “could make immune escape worse than what we’re seeing now” with BA.5 and BA.4, both of which are subvariants known to evade immunity from both vaccination and prior infection.

https://twitter.com/EricTopol/status/1543975036578435073

BA.2.75 was first detected in India in early June. Along with the usual Omicron mutations, it has as many as nine additional changes, none of which are concerning individually. “But all appearing together at once is another matter,” Tom Peacock, a virologist at the Department of Infectious Disease at Imperial College in London, said recently in a tweet.