Marr and her collaborators are among the few other labs with the means and expertise to do such work. In a study published last October, her team measured the different sizes of particles coming out of sick hamsters’ lungs. They found that SARS-CoV-2 congregated in the smallest aerosols; particles smaller than 5 microns contained the majority of airborne virus. “It’s a little counterintuitive because we think, ‘Oh, well, larger particles have a lot larger volume and should carry a lot more virus,’ but that doesn’t seem to be the case.”

Now, humans aren’t hamsters. But an aerobiologist at the University of Maryland, Don Milton, has been using a medieval-looking device he invented called the Gesundheit II to measure the amount of SARS-CoV-2 inside the breath of infected college students and staff. In a study published in September, his team found more virus inside smaller versus larger particles.

They also discovered that SARS-CoV-2 was evolving to be even better at getting into those smaller particles. People infected with the Alpha strain (previously known as B.1.1.7, which first emerged in the U.K.) shed 18 times more viral material into fine aerosols than people infected with older strains, after controlling for overall differences in viral load. Milton’s team is now looking at newer, even more contagious variants like Delta and Omicron.