On Apr. 24, 2020, a new study led by researchers at Oxford and Guangdong Centre for Diseases Control and Prevention describes the epidemiology and genetic make-up of the COVID-19 outbreak in Chinaﾒs most populous region, and shows how early and intensive testing and tracing helped to interrupt local transmission of the virus. Analysing genomes generated from infected individuals, the researchers established that the outbreak in Guangdong was not caused by one large chain of transmission, but instead there were hundreds of independent introductions from outside the Province.