Fig. 2: Selection of antigens for the SONIA neutralization PCR test.

Both S1 subunit and receptor binding domain (RBD) of spike protein have the ability to engage with the ACE2. To evaluate suitability for the neutralization PCR assay, we tested convalescent COVID-19 patient sera (N = 2, blue circle) and healthy donor sera (N = 4, red circle) collected prior to the outbreak. The COVID-19 sera were confirmed to harbor NAb by a pseudo-virus neutralization assay. The y-axis is the SONIA neutralization PCR test signal Δ\(\overline{{Ct}}\) calculated by subtracting the Ct value of the sample from that of a buffer only blank control.