In phase 1 (A and C) SARS-CoV-2 RBD-specific IgG antibodies were detected on day 14 in 88.9% of participants injected with only rAd26-S and in 84.2% of participants with rAd5-S. At day 21, RBD-specific IgG were detected in all participants.

In phase 2 (B and D) SARS-CoV-2 RBD-specific IgG antibodies were detected in 85% of participants on day 14 and in 100% on day 21. The boosting component (rAd5) led to an increase in IgG titres. 100% of participants produced neutralising antibodies to SARS-CoV-2 with both rAd26-S and rAd5-S.