What’s happening: The WHO recently labeled Mu (B.1.621 and first discovered in Colombia) a variant of interest as preliminary data indicated it may better elude immunity from prior infection or vaccination.

Mu may “indicate potential properties of immune escape, as it has some of these hallmarks of being able to get around that existing vaccine protection, but it doesn’t mean that’s what we’re seeing play out in real life,” says Anne Rimoin, an epidemiologist and director of the UCLA Center for Global and Immigrant Health.

Fauci says when comparing how specific variants may escape antibody protection, Beta appears more evasive than Mu, and Mu more than Delta.

Only about 0.5% of new cases are showing as Mu, Fauci says, with 99.3% testing as Delta, which has such an “extraordinary ability” to transmit that it won’t likely lose its global dominance in the immediate future.