During the pandemic, research has pointed to the likelihood that aerosols—made up of tiny droplets of water even smaller than those from a cough—may carry SARS-CoV-2, the novel coronavirus that causes COVID-19. Because aerosols can linger in the air in enclosed spaces, this research has important implications for prevention. But until July 7, the World Health Organization had declined to acknowledge that aerosol-borne particles could transmit the virus.