Administration of ARVAC CG booster increases the nAb titers against the Ancestral, Gamma, Delta, Omicron BA.1 and Omicron BA.5 variants of SARS-CoV-2.
The nAb titers against the Ancestral, Gamma, Delta and Omicron BA.1 and Omicron BA.5 variants of SARS-CoV-2 in plasma samples of individuals boosted with ARVAC CG 25 µg (Seroconversion rates were evaluated as the percentage of subjects with at least a fourfold increase (4×-seroconversion rates) or a tenfold increase (10×-seroconversion rates) in the nAb titers at a specific timepoint respect to baseline values. After 14 days of a booster with ARVAC CG the 4×-seroconversion rates for the Ancestral SARS-CoV-2 strain were 88.3 % (95% CI, 77.8–94.2) in the 25 µg cohort and 90.0% (95% CI, 69.9–98.2) in the 50 µg cohort. Whereas the corresponding 4×-seroconversion rates were 90.0% (95% CI, 79.8–95.3) and 85% (95% CI, 64.0–94.8) against the Gamma VOC, 80.0% (95% CI, 68.2–88.2) and 85.0% (95% CI, 64.0–94.8) for Delta VOC, 93.3% (95% CI, 84.1–97.4) and 85.0% (95% CI, 64.0–94.8) for Omicron BA.1 VOC, and 80.0% (95% CI, 68.2–88.2) and 80.0% (95% CI, 58.4–91.9) for Omicron BA.5 VOC, respectively (Supplementary Table Fourteen days after boosting, 4×-seroconversion rates for all tested variants were similar in both dosage groups, while 10×-seroconversion rates for Omicron BA.1 VOC were significantly higher in the 50 µg cohort (Supplementary Table Based on pre-existing anti-N IgG titers and/or previous history of COVID-19, individuals were stratified into two populations: seronegative individuals with no previous COVID-19 history and seropositive and/or with previous history of COVID-19 individuals. Both populations developed similar nAb GMTs against Ancestral, Gamma, Delta, Omicron BA.1 and Omicron BA.5 after 14 days of ARVAC CG booster. Moreover, GMFR from baseline were similar for both populations in groups A and B either when analyzed in all individuals of each group (Supplementary Fig. No significant differences were found in the nAb responses and seroconversion rates between female or male volunteers, except for the 4×-seroconversion rate in nAbs against Delta VOC (Supplementary Table When volunteers were subdivided regarding the primary vaccination received, a significant increase in the nAb GMTs against the different viral variants was observed in all previously vaccinated subgroups (Fig. 