Given it was in the US at least in December 2019 if not earlier according to the NIH retrospective serology study it doesn't seem to be completely impossible. https://www.nih.gov/news-events/news-releases/nih-study-offe... Also similar Italian serology study by National Cancer Institute showed that sars-cov-2 was circulating in Italy as early as September 2019. https://www.reuters.com/article/us-health-coronavirus-italy-...