The Delta variant of SARS-CoV-2 (B.1.617.2) became the dominant variant in the United States over the summer of 2021, and there are fears that another, potentially more dangerous, variant could follow (New Atlas, Newsweek). The CDC estimates proportions of SARS-CoV-2 lineages circulating in the United States, grouped in two-week intervals, here: https://covid.cdc.gov/covid-data-tracker/#variant-proportions. For the period ending 17 July 2021, the Delta variant and three sublineages (e.g., AY.1) represented a combined 83.5% percent share of COVID lineage in the US as of the launch of this question. Data from the “Nowcast” option would count, and Delta sublineages would not count.

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NOTE 13 December 2021: As the CDC has changed from two-week to one-week intervals, the question would close upon a variant other than Delta next representing more than 70.0% for a one-week period within the range covered by the appropriate bin.

NOTE 14 December 2021: To further clarify the clarification note dated 13 December 2021, we are revising the remaining bins to align with the CDC's current practice. The third bin is now "A one-week period ending between 27 November 2021 and 15 January 2022." The fourth bin is now "A one-week period ending between 22 January 2022 and 12 March 2022."

The question closed "A one-week period ending between 27 November 2021 and 15 January 2022" with a closing date of 19 December 2021.

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