Jan. 2, 2020
Retrospective testing in Ohio found that five women and a man who had developed Covid-like symptoms in early January had antibodies for the virus, qualifying as “probable” infections. They lived at opposite corners of the state, up to 200 miles apart. Though the findings aren’t conclusive, modeling experts say they are consistent with the speed of the pandemic’s later spread.

Jan. 17, 2020
Screening began on air travelers, but only those coming from Wuhan, China, where the virus emerged, and only at airports in San Francisco, Los Angeles and at New York’s JFK. A handful of sick people were identified, but scientists say more were missed. By the end of January, more than half a million people flew from China to the U.S…

Jan. 25, 2020
By now the virus was likely spreading to 10 new people every day in California, according to estimates from researchers at Northeastern University’s Network Science Institute.