The World Health Organization has identified the B.1.621 variant as a variant of interest (VOI), assigning it the ‘Mu’ letter from the Greek alphabet on August 30.

VOI is a lesser classification than variant of concern (VOC), which denotes a strain that is highly virulent and/or able to impinge preexisting public health measures such as vaccines, diagnostics, or therapeutics. Current VOCs include the Alpha, Beta, Gamma, and Delta variants.