“It is striking that this [B.1.1.7] lineage may already have been established in the US for some 5-6 weeks before B.1.1.7 was first identified as a variant of concern in the UK in mid-December¹⁵. And it may have been circulating in the US for close to 2 months before it was first detected, on 29 December 2020.

B.1.1.7 viruses have been estimated to account for only 0.3% of SARS-CoV-2 cases nationally as of early January 13.

It is also worth noting the vast majority (>90%) of US B.1.1.7 cases appear to be generated in these well-established domestic outbreaks rather than via travel-related introductions from the UK or other affected countries, though such cases are surely also happening.”

https://virological.org/t/phylogenetic-evidence-that-b-1-1-7-has-been-circulating-in-the-united-states-since-early-to-mid-november/598

Image by Gerd Altmann from Pixabay