http://www.sciencemag.org/news/2020/03/would-everyone-wearing-face-masks-help-us-slow-pandemic

Science’s COVID-19 reporting is supported by the Pulitzer Center.

As cases of coronavirus disease 2019 (COVID-19) ballooned last month, people in Europe and North America scrambled to get their hands on surgical masks to protect themselves. Health officials jumped in to discourage them, worried about the limited supply of masks for health care personnel. “Seriously people-STOP BUYING MASKS!” began a 29 February tweet from U.S. Surgeon General Jerome Adams. The World Health Organization and U.S. Centers for Disease Control and Prevention (CDC) have both said that only people with COVID-19 symptoms and those caring for them should wear masks.