Evidence from the CDC and contemporaneous reporting shows that the SARS‑CoV‑2 Delta variant did in fact become the dominant strain in the U.S. within a few months of July 2021.

Key points:

• On June 15, 2021, CDC Director Rochelle Walensky stated that the Delta variant was expected to become the dominant strain in the U.S., noting it was already rapidly increasing as a share of cases.
• CDC genomic surveillance data and multiple news summaries report that by early July 2021, Delta had already become the dominant variant nationally (surpassing 50% of sequenced cases), and by mid‑July 2021 it accounted for an even larger majority of U.S. infections.
• Thus, Sacks’ prediction that “delta variants can become the main the dominant strain if it isn't already” was borne out almost immediately after (and arguably already at) the podcast’s release date of 9 July 2021.

Because the Delta variant did indeed become (and remain for some time) the dominant SARS‑CoV‑2 strain in U.S. circulation in the near term after July 2021, this prediction is right.