Cross-neutralization of antibodies induced by inactivated SARS-CoV-2 vaccine against Beta and Delta variants

ABSTRACT

Objective To evaluate the in vitro cross-neutralization of serum antibodies in human and mice immunized with inactivated SARS-CoV-2 vaccine against Delta and Beta variants. Methods Human serum samples after a second and a third dose of inactivated SARS-CoV-2 vaccine and mouse serum samples after a two-dose vaccination were collected. The neutralizing antibodies in the samples against SARS-CoV-2 strains of prototype, Delta and Beta variants were detected using micro-neutralization assay in biosafety level III laboratory. The seroconversion rates and geometric mean titers (GMTs) of antibodies were calculated. Results The seroconversion rates of antibodies in human serum samples against different SARSCoV-2 strains were all above 95%. After two-dose vaccination, the GMTs of neutralizing antibodies against the prototype, Delta and Beta strains were 109, 41 and 15, respectively. The GMTs decreased by 2. 7 folds and 7. 3 folds for the Delta and Beta variants as compared with the prototype strain. After the booster vaccination, the GMTs of neutralizing antibodies against the prototype, Delta and Beta strains were 446,190 and 86, respectively. The GMTs of neutralizing antibodies against Delta and Beta variants decreased by 2. 3 folds and 5. 2 folds as compared with that against the prototype strain. The seroconversion rates of antibodies against different SARS-CoV-2 strains in mouse serum samples were all 100%. The GMTs of neutralizing antibodies against the prototype, Delta and Beta strains were 2 037, 862 and 408, respectively. The GMTs decreased by 2.4 folds and 5.0 folds for the Delta and Beta variants. Conclusions Inactivated SARS-CoV-2 vaccine could induce a certain level of neutralizing antibodies against Delta and Beta variants in both human and mouse models. Moreover, a third dose of vaccine induced higher levels of neutralizing antibodies against Delta and Beta variants in human. This study provided valuable data for the clinical application and protective evaluation of the inactivated SARS-CoV-2 vaccine.