Pseudovirus based neutralization assay
Serum samples were diluted in DMEM-5 (reduced serum media; 5% FBS, 1% L-glutamine, 1x MEM NEAA) from 1:30 to 1:2430. SARS-CoV-2 Spike pseudotyped VSV-ΔG virus was diluted in DMEM-5 to a final concentration of 10-4 TU/ml. 100 µl diluted serum and 50 µl diluted virus were mixed in a 96 well plate and incubated in 370C incubator for 1 hr. Then, serum-virus mixture was added to Vero E6 adherent cells (80% confluent) and incubated in a 5% (v/v) CO2, 37 °C incubator for 2 days. Cells were fixed with 4% PFA and analyzed by using Tecan plate reader (Infinite M200 Pro, Life Science). The GFP fluorescence intensity was microscopically detected at 48 hours post-infection by Axio Observer Fluorescence Microscope (Zeiss).