CDC modeling estimated about 120 million cumulative SARS‑CoV‑2 infections in the U.S. by May 2021 and about 150 million by September 2021, meaning roughly 30 million people (≈9% of the ~331 million population) were newly infected over that interval.(en.wikipedia.org) Genomic surveillance shows that Delta rose from about 1% of circulating viruses in early May 2021 to >95–99% by late July and remained at that level through early December 2021, so nearly all infections during the late‑summer and fall “Delta wave” were caused by Delta.(cdc.gov) Independent blood‑donor serosurveys also find that infection‑induced seroprevalence increased from about 20.2% in May 2021 to 28.8% in December 2021, implying roughly an 8–9 percentage‑point rise in the share of the population ever infected during the period when Delta was predominant.(pmc.ncbi.nlm.nih.gov) Taken together, these data suggest that on the order of 8–10% of the U.S. population was infected during the Delta wave, which fits within Friedberg’s stated ceiling of “up to ~10%,” so the prediction is broadly accurate (acknowledging some uncertainty in precisely attributing infections to Delta).