To test the luciferase expression within cells after infection with rZHDNSs-hRLuc, Vero E6 cells were infected using a MOI of 0.3 and 3. Next, every 2 h, for 12 h, luciferase activity was measured in triplicates by Renilla Luciferase Assay System (Promega, Madison, WI). To check the stability of luciferase expression through passages, Vero E6 cells were infected using an MOI of 3 and the luciferase activity was measured in triplicates at 8 h postinfection.