On New Year’s Eve, Helen Branswell, a reporter at the science and medical news website Stat, was finishing an article about the development of an elusive Ebola vaccine when she got an inkling of her next big story.

“Hopefully this is nothing out of the ordinary,” she wrote on Twitter, adding a link to a report of an “unexplained pneumonia” in central China.

Two days later, she tweeted a South China Morning Post article about the outbreak and wrote, “Not liking the look of this.”

Stat published Ms. Branswell’s first article on the “growing cluster of unexplained pneumonia cases” on Jan. 4. There was some indication, she reported, of “a new virus, and perhaps even a new coronavirus.”