Seroconversion and Abundance of IgG Antibodies against S1-RBD of SARS-CoV-2 and Neutralizing Activity in the Chilean Population

COVID-19 is a pandemic caused by SARS-CoV-2. In Chile, half a million people have been infected and more than 16,000 have died from COVID-19. As part of the clinical trial NCT04384588, we quantified IgG against S1-RBD of SARS-CoV-2 (anti-RBD) in recovered people in Santiago and evaluated their suitability as COVID-19 convalescent plasma donors. ELISA and a luminescent SARS-CoV-2 pseudotype were used for IgG and neutralizing antibody quantification. 72.9% of the convalescent population (468 of 639) showed seroconversion (5-55 μg/mL anti-RBD IgG) and were suitable candidates for plasma donation. Analysis by gender, age, and days after symptom offset did not show significant differences. Neutralizing activity correlated with an increased concentration of anti-RBD IgG (p < 0.0001) and showed a high variability between donors. We confirmed that the majority of the Chilean patients have developed anti-SARS-CoV-2 antibodies. The quantification of anti-RBD IgG in convalescent plasma donors is necessary to increase the detection of neutralizing antibodies.