Analysis of the specificity of the immune response induced by MVA-S and MVA-ST revealed a differential bias towards the S1 and S2 subunits of the S-protein: Both MVA-S and MVA-ST increased the S2-specific IgG levels that were already detectable at baseline, possibly as a result of cross-reactive antibodies and memory cells from previous infections with common cold coronaviruses, as has been suggested previously33–35. The gene discussed is PROS1; the disease is infection.