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.

Currently the predominant SARS-CoV-2 variant in the U.S. is Delta, which for the week ending 20 November was estimated to make up 99.9% of all sequenced SARS-CoV-2 cases.

When will Omicron become the predominant SARS-CoV-2 variant in the U.S.?

This question will resolve to the date that the Omicron variant of SARS-CoV-2 makes up more than 50% of estimated cases of COVID-19 in the United States. Resolution will come from credible statements by the CDC or WHO. To remain aligned with the original criteria of this question, if the date when Omicron becomes the dominant variant is estimated to be on a day between Monday to Saturday (in the US), this question will resolve on the Sunday preceeding it. Resolution may be delayed to verify the claims of Omicron's prevalence.

If this does not occur by July 1, 2022, it resolves as > July 1, 2022.

[Dec 22, 2021 - casens: The resolution criteria have been changed. The previous criteria are in the fine-print]

Resolution criteria from before December 22, 2021:

This question will resolve on the basis of the U.S. CDC's “Variant Proportions" Nowcast, which updates every Tuesday to show estimates for the previous week (Sunday-Saturday). This will resolve as the Sunday of the first week for which the Omicron variant is predominant in the U.S., meaning it makes up >50.0% of all sequenced SARS-CoV-2 cases for that week (this would be reflected in the Tuesday update of the following week).

For example, if the Nowcast estimate for the week starting Sunday, 14 November and ending Saturday, 20 November had shown >50% Omicron, and this was reflected in the Tuesday 23 November update, then this question would resolve as Sunday, 14 November.

Thank you to Nathan Young, Clay Graubard, David Manheim, Philipp Schoenegger, and Edward Saperia for their question suggestions and input.