During the early months of the COVID-19 pandemic, Virginia Tech aerosol scientist Linsey Marr and her colleagues met with the World Health Organization to warn them about airborne virus spread. At the time, the organization ignored their warning, insisting that the coronavirus disperses primarily through droplets that did not hang in the air and fell quickly to the ground. Their droplet argument led to guidelines centered around hand washing and social distancing rather than mask use. The WHO’s initial guidance was based on a misinformed definition of aerosols which specified that all infectious particles smaller than 5 microns are aerosol spread, while anything larger than 5 microns is a droplet. “Reality is far messier,” wrote Molteni, “with particles much larger than 5 microns staying afloat and behaving like aerosols, depending on heat, humidity, and airspeed.” Marr had a feeling the misunderstanding was a symptom of a deeper issue, that “outdated science was underpinning public health policy.” In a riveting story, Molteni follows Marr on her mission to track down the incorrect distinction between droplets and aerosols. She and her colleagues follow the 5-micron standard back to a Harvard engineer named William Firth Wells, whose work included a study that used the 5-micron benchmark for tuberculosis spread. Yet his research also showed that particles as large as 100 microns could spread quite readily as aerosols. “Over time, through blind repetition, the error sank deeper into the medical canon,” Molteni wrote. “A powerfully-told and important story,” said BBC producer Cathy Edwards. “Megan Molteni skillfully conveyed the dangers of falling back on mistaken dogma, and the human endeavor involved in upturning these false assumptions.” Molteni said the COVID-19 pandemic “revealed in stark terms how science, like all human endeavors, is messy, political, and ever-evolving. I’m grateful to the researchers whose perseverance to amend flawed public health policies saved an untold number of lives, and to my editors for trusting me to tell their story during one of the most challenging years our profession has ever faced.”