Graphical AbstractHighlights d SARS-CoV-2 uses the SARS-CoV receptor ACE2 for host cell entry d The spike protein of SARS-CoV-2 is primed by TMPRSS2 d Antibodies against SARS-CoV spike may offer some protection against SARS-CoV-2

Coronavirus disease 2019 (COVID -19) is an acute infection of the respiratory tract that emerged in late 2019 1,2 . Initial outbreaks in China involved 13.8% of cases with severe courses, and 6.1% of cases with critical courses 3 . This severe presentation may result from the virus using a virus receptor that is expressed predominantly in the lung 2,4 ; the same receptor tropism is thought to have determined the pathogenicity-but also aided in the control-of severe acute respiratory syndrome (SARS) in 2003 5 . However, there are reports of cases of COVID-19 in which the patient shows mild upper respiratory tract symptoms, which suggests the potential for pre-or oligosymptomatic transmission 6-8 . There is an urgent need for information on virus replication, immunity and infectivity in specific sites of the body. Here we report a detailed virological analysis of nine cases of COVID-19 that provides proof of active virus replication in tissues of the