Serum-neutralizing antibodies detection
The neutralizing antibodies against the prototype strain of SARS-CoV-2 (SARS-CoV-2/human/CHN/CN1/2020, GenBank number MT407649.1) and variants Beta (B.1.351), Gamma (P.1) and Delta (B.1.617.2) were quantified using a microcytopathogenic effect assay according to previous trials (