My understanding is that the PCR test doesn't reliably distinguish between variants but can detect all variants. If a sample tests positive in PCR it's then sent on for genomic sequencing and that does distinguish between all variants.
However this was published in the Guardian on 7th of December - I've seen nothing more about it so can't say whether it's reliable information or not...
`Scientists find ‘stealth’ version of Omicron that may be harder to track: Variant lacks feature that allows probable cases to be distinguished among positive PCR tests' LINK
`Scientists say they have identified a “stealth” version of Omicron that cannot be distinguished from other variants using the PCR tests that public health officials deploy to gain a quick picture of its spread around the world....The stealth variant has many mutations in common with standard Omicron, but it lacks a particular genetic change that allows lab-based PCR tests to be used as a rough and ready means of flagging up probable cases. The variant is still detected as coronavirus by all the usual tests, and can be identified as the Omicron variant through genomic testing, but probable cases are not flagged up by routine PCR tests that give quicker results.
`The discovery of the new form of Omicron prompted researchers to split the B.1.1.529 lineage into standard Omicron, known as BA.1, and the newer variant, known as BA.2. “There are two lineages within Omicron, BA.1 and BA.2, that are quite differentiated genetically,” Prof Francois Balloux, the director of the University College London Genetics Institute, said. “The two lineages may behave differently.”.'..
