Tests of the US blood supply indicates the SARS-CoV-2 IgG antibodies were present in the US in late December 2019, around 2 weeks prior to January 7, 2020 when the blood was taken, earlier than the official first case of COVID-19. These IgG antibodies do not appear until about two weeks post infection, placing infection date around December 24, 2019.
The US flu season was “very high” in December 2019 to early 2020.