Who infected whom?

China strikes back:

The result indicated that, for the 12 US states, the possible dates of the first infection, with a probability of 50 per cent, fall mostly between August and October 2019, while the earliest is April 26, 2019 on Rhode Island, and the latest is Nov 30, 2019 in Delaware.

All of the dates indicated by the data are earlier than Jan 20, 2020, the officially announced date of the first confirmed case in the United States, showing that the Covid-19 pandemic in the United States started to spread around September 2019 with a high confidence probability.

The result also showed that the date of the first Covid-19 case in Wuhan, with a probability of 50 percent, is Dec 20, 2019, and the date for Zhejiang is Dec 23, 2019. It infers that the Covid-19 in China is most likely to have started in late December 2019.

https://www.straitstimes.com/world/united-states/covid-19-might-have-started-to-spread-in-sept-2019-in-the-us-chinese-study