The Omicron offshoot carries more than 35 mutations in key portions of the virus compared with XBB.1.5, the dominant variant through most of 2023 - a number roughly on par with the Omicron variant that caused record infections compared to its predecessor.

A dozen scientists around the world said while it was important to monitor BA.2.86, it was unlikely to cause a devastating wave of severe disease and death given immune defenses built up worldwide from vaccination and prior infection.