To assess the viral growth, the recombinant viruses were inoculated at a multiplicity of infection (MOI) = 0.1 in Huh7-ACE2 cells and Vero-TMPRSS2 cells, respectively, and then the culture supernatants were collected at 6, 12, and 24 h post infection to determine the viral RNA and the viral titer. Here, ACE2 is linked to infection.