Transmission through aerosols matters — and probably a lot more than we’ve been able to prove yet.

Finally. The World Health Organization has now formally recognized that SARS-CoV-2, the virus that causes Covid-19, is airborne and that it can be carried by tiny aerosols.

As we cough and sneeze, talk or just breathe, we naturally release droplets (small particles of fluid) and aerosols (smaller particles of fluid) into the air. Yet until earlier this month, the W.H.O. — like the U.S. Centers for Disease Control and Prevention or Public Health England — had warned mostly about the transmission of the new coronavirus through direct contact and droplets released at close range.

The organization had cautioned against aerosols only in rare circumstances, such as after intubation and other medical procedures involving infected patients in hospitals.