On 25 November, South Africa announced that it was tracking a new variant, B.1.1.529/Omicron, and shared the following:

• New variant detected in South Africa (lineage B.1.1.529) with high number of mutations, which are concerning for predicted immune evasion and transmissibility
• B.1.1.529 genomes produced from samples collected 12-20 Nov from Gauteng, SA (n=77), Botswana (n=4) and Hong Kong (n=1, traveler from SA)
• B.1.1.529 can be detected by one particular PCR assay (before whole genome sequencing)
• Early signs from diagnostic laboratories that B.1.1.529 has rapidly increased in Gauteng and may already be present in most provinces
• Mutation profile predicted to give significant immune evasion and enhanced transmissibility

See also these three assessments by the UK HSA, Belgian NRL, and WHO respectively.

Some have suggested that SARS-CoV-2 vaccines may have to be updated to target the Omicron variant in particular, given that its unique constellation of mutations may result in lower vaccine- and infection-elicited antibody neutralization. Vaccine producers including Moderna, Pfizer/BioNTech, Janssen, and Novavax have said they are testing their vaccines against the new variant. Moderna has announced it is advancing an Omicron-specific booster candidate.

Will the US, UK, or EU authorize an Omicron-specific booster before 2023?

This question will resolve on the basis of whether the U.S. FDA, UK MHRA, or EU EMA authorize an Omicron-specific booster before 2023.

An Omicron-specific booster must be specially formulated to specifically target the genetic sequence of the Omicron variant.

The booster dose formulation can also include formulations that target other variants (e.g., Delta) so long as the Omicron variant is specifically targeted as well.

Multi-valent booster candidates, such those being developed by Moderna, would count toward positive resolution so long as they target at least 8 spike mutations that Omicron has accrued relative to the original Wuhan-Hu-1 sequence. In the case of Moderna, this would mean that: the mRNA-1273.211 multi-valent candidate that targets 4 of Omicron's spike mutations would not count toward positive resolution, while the mRNA-1273.213 multi-valent candidate that targets 8 of Omicron's spike mutations would count.