Processing of serum samples
HEAT
Serum samples were collected in serum-gel tubes (Sarstedt) by venipuncture. After that, the samples were transported at 4 °C and processed within 48 h. After centrifugation, the serum was transferred to 2 ml cryotubes and stored at −80 °C till use. For further analysis in serological assays, the samples were thawed at room temperature, and 0.5 ml of each sample was pipetted into a 7 ml screwing tube (Sarstedt). For analysis in the pseudovirus neutralization assay, the samples were heat inactivated after thawing and processed as described below.