Molecular model of a coronavirus inhibitor drug (blue) bound to a viral protein. The protein (orange) is an enzyme called coronavirus main protease (Mpro), which the virus uses to produce proteins needed for its replication. Inhibiting this enzyme could be an effective way of stopping diseases caused by the virus. Coronaviruses cause a number of diseases, including the common cold, pneumonia and the new respiratory disease that emerged in Wuhan, China, in December 2019. This new disease, officially called coronavirus disease 2019 (COVID-2019), is caused by a new form of the virus, now named SARS-CoV-2019. Like the 2003 SARS outbreak, it is a respiratory disease that is fatal in some cases, particularly in patients with existing conditions.