SARS-CoV-2-specific neutralising antibody levels were measured in duplicate with the MN test in a BSL-3 laboratory. The serum samples were heat-inactivated at 56 °C for 30 min and 2-fold serially diluted starting from 1:4 in EMEM supplemented with 2% of heat-inactivated FBS and antibiotics. Fifty plaque‐forming units (PFU) of the SARS-CoV-2/Finland/1/2020 strain were added to the serum dilutions and incubated for 1 h at 37 °C. Vero E6 cells (5 × 104/well) were added to the virus–serum mix, and the mixture was incubated in 96-well plates for 4 days at 37 °C with 5% CO2. Neutralisation was assessed by CPE. The neutralisation endpoint was determined as the 50% endpoint of the serum that inhibited the SARS-CoV-2 infection observed by CPE of inoculated cells.