Figure 2.

Spike protein inhibitory assay—neutralizing antibodies. Immunoglobulin neutralizing activity was measured by SPIA kit (DiaMetra Srl) at the baseline (T0), after the first dose of vaccine (T1) and after the booster (T2). Results are expressed as the percentage of inhibition of the binding of peroxidase-labeled ACE2 receptor to RBD-coated plates. After the second dose, all the subjects show higher neutralizing activity with respect to T1 and T0. Bars represent Median and interquartile range (IQR). The empty triangles represent the two vaccinated convalescent subjects. In these ones, high neutralizing ability is already achieved after the first dose.