In early February 2020, China locked down more than 50 million people, hoping to hinder the spread of a new coronavirus. No one knew at the time exactly how it was spreading, but Lidia Morawska, an expert on air quality at Queensland University of Technology in Australia, did not like the clues she managed to find.

It looked to her as if the coronavirus was spreading through the air, ferried by wafting droplets exhaled by the infected. If that were true, then standard measures such as disinfecting surfaces and staying a few feet away from people with symptoms would not be enough to avoid infection.

Dr. Morawska and her colleague, Junji Cao at the Chinese Academy of Sciences in Beijing, drafted a dire warning. Ignoring the airborne spread of the virus, they wrote, would lead to many more infections. But when the scientists sent their commentary to medical journals, they were rejected over and over again.