There have been hundreds of viruses sequenced from infections in the USA. We can use these sequences to date the arrival of the epidemic. Doing so, we see that there were multiple introductions driving the US epidemic and the earliest was in Jan. https://t.co/gbqIAFTkgc 11/18 pic.twitter.com/r2uylqcH2D

— Trevor Bedford (@trvrb) April 12, 2020