"In December 2019, COVID-19 was launched in the United States. CDC research shows that isolated infections occurred in the western region of the United States in mid-December. Antibodies were also found in other states in early January, and only then did they know that the virus had been introduced into these.local.Scientists pointed out that this antibody is unlikely to develop to inhibit other coronaviruses, because 84 samples were found to have neutralizing activity against SARS-CoV-2.
https://fortune.com/2020/12/01/december-2019-covid-arrival-us/