Result:
A total of 88 volunteers aged 27.0±5.0 years old were recruited, including 20 males and 68 females. Among them, 29 participants had accepted vaccine A and 59 participants had received vaccine B (Supplementary Table 1). All the sera samples were collected within 2 months, from whom were immunized with the inactivated vaccine as boosters post two-dose inactivated immunization (Supplementary Table 1). The pseudotyped strains of SARS-Cov-2 Prototype, Omicron BA.1 and BA. 5 variants were constructed. (Figure 1A)
The geometric mean titers (GMT) of the serum pseudovirus neutralization test for Omicron BA.1 and BA.5 variants were 60 and 42, which were decreased by 6.2-fold and 8.0-fold compared with the prototype strain respectively (GMT, 331) (Supplementary Table1, Figure 1C). The overall comparison of neutralizing titres against each variant showed significant differences between the prototype and Omicron variants is shown in Figure 1C. The neutralization activities against the prototype, Omicron BA.1 and BA.5 variants in serum from participants that had received vaccine A were similar to those of participants that had received vaccine B (Supplementary Figure 1B).
Using ELISA test, the GMT of IgG tiers against the S of the prototype, Omicron BA.1 and BA.5 variants were 2797, 2334 and 2447 respectively (Supplementary Table 1), which showed no significant difference between the prototype and Omicron variants (Figure 1B). In addition, the IgG titers against Omicron BA.1 and BA.5 variants in serum from participants that had received vaccine A, were similar to those of participants that had received vaccine B, as well as the prototype (Supplementary Figure 1A).
The neutralization-positive rates of serum against the pseudovirus strains of SARS-Cov-2 Prototype, Omicron BA.1 and BA.5 variant were 100% (88/88), 95.45% (84/88) and 92.04% (81/88) respectively (Table 1). And the IgG binding positive rates to S of SARS-Cov-2 Prototype, Omicron BA.1 and BA.5 variant were all 100% (Table 1). All 88 serum samples testing positive by ELISA were also anti S of SARS-Cov-2 prototype positive by pseudovirus-based neutralization assay, corresponding to a positive agreement rate of 100% (88/88). For SARS-Cov-2 Omicron variants BA.1 and BA.5, the positive agreement rates of the two test methods were 95.45% (84/88) and 92.05% (81/88), respectively.
We also assessed the correlation between neutralizing antibody titers and IgG titers by using Pearson correlation analysis. The strongest correlation was observed between IgG binding activities to S of prototype by ELISA and the titers of neutralizing antibodies (rs=0.8238 , p<0.0001 ) (Figure 2). The analysis also revealed statistically significant association between the IgG titers of anti S of SARS-Cov-2 Omicron BA.1 variant and neutralizing antibody titers with ND50 values (rs=0.7000 , p<0.0001 ). (Figure 2). A minor correlation was found between two methods in SARS-Cov-2 Omicron BA.5 variant (rs=0.5499 ,p<0.0001 ).