While there may have been a few cases outside Wuhan as early as December, it appears the virus did not become widespread until months later
Source:
https://www.newscientist.com/article/mg24733013-800-when-did-the-coronavirus-really-reach-the-us-and-europe/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home