Neutralization assay cytopathic effect-based assay (CPE)
To determine the neutralizing ability and capacity of vaccine induced antibodies a CPE assay was performed using wild-type SARS-CoV-2 (SARS-CoV-2/ABS/NL20). Serum samples were heat-inactivated for 30min at 56°C. Two-fold serial dilutions were prepared starting at 1:20 up to 1:160. 100 TCID50 of the virus was added to each well and incubated for 37°C for 1h. The mixture has been added on a monolayer of Vero cells and incubated again for 37°C for 4 days. Four days later the cells were inspected for cytopathic effect. The titer was expressed as the highest dilution that fully inhibits formation of CPE.