What is the BA.2 or “stealth” Omicron subvariant?

The World Health Organization (WHO) is currently monitoring the original Omicron variant, BA.1, along with several additional subvariants BA.1.1, BA.2 and BA.3. The subvariant BA.2 has been referred to as “stealth” Omicron because it has genetic mutations that could make it harder to distinguish from the Delta variant using PCR tests as compared to the original version of Omicron.