COVID-19 is transmitted by aerosols. (AKA it’s airborne.)
Aerosols are extremely small, light micro-droplets that can float in the air for a long time. Lots of research over the past year has shown that the coronavirus can be transmitted by these tiny particles.
Interested in learning more about how these droplets can cause infection? This post from First10EM explains this kind of COVID-19 transmission happens, and includes links to related studies.