A Vero E6 cells were infected with SARS-CoV-2, pre-incubated with indicated concentrations of the neutralizing VHH-72 Cells were fixed two days after inoculation, stained with sets of anti-RBD (green) and anti-S1ΔRBD (red) nanobodies and analyzed by CLSM. We used a cocktail of such fluorophore-labeled VHH antibodies to ensure that negative fluorescence readings truly indicated neutralization and thus absence of viral infection and not just masking of the IF epitope by the tested nanobody. 