“It’s possible but I wouldn’t say it’s very likely,” said Dr. William Haseltine, president of the global health think tank ACCESS Health International and former Harvard Medical School professor, who recently chaired the U.S.-China Health Summit in Wuhan, in an interview with The Daily Beast.

Those who lived in current COVID-19 hot spots back in the fall and had recently travelled from Wuhan or hard-hit areas in Europe, had an unusually bad cold with a prolonged fever, were tested for the flu and had the results come back negative—“maybe they had this,” was as far as Haseltine would go. But he remained skeptical that there were very many, if any, such cases that had not yet been detected.

“There is zero probability [SARS-CoV-2] was circulating in fall 2019,” tweeted Trevor Bedford, a computational biologist at Fred Hutchinson Cancer Research Center who has been tracking the virus’s genetic code as it has spread through the country.