The antiviral activity of CQ against MERS-CoV and HCoV-229E was assessed in the human hepatoma cell line (Huh-7) and found that the 50% effective concentrations (EC50) were 3.0(±1.1) μM and 3.3(±1.2) μM, the 50% cytotoxic concentrations (CC50) were 58.1(±1.1) μM and >50, and the selectivity indexes (SI; calculated as CC50/EC50) were 19.4 and >15, respectively [10]. CQ could inhibit an early step in the MERS-CoV replication cycle. Addition of CQ to VeroE6 cells 1 h after MERS-CoV infection did not affect virus production. However, when CQ was added 1 h before MERS-CoV infection, 16 μm and 32 μM concentrations of CQ could reduce the virus production of 1-log and 2-log, respectively [10].