Prevalence of Severe Acute Respiratory Syndrome Coronavirus 2 Neutralizing Antibodies in Egyptian Convalescent Plasma Donors

Using convalescent plasma as immunotherapy is an old method for treatment of infectious diseases. Several countries have recently allowed the use of such therapy for the treatment of COVID-19 patients especially those who are critically ill. A similar program is currently being tested in Egypt. Here, we tested 227 plasma samples from convalescent donors in Egypt for neutralizing antibodies against SARS-CoV-2 using a microneutralization assay. A third of the tested samples did not have antibody titers and 58% had titers between 1:10 and 1:80. Only 12% had titers > 1:160. We also compared microneutralization assays using different virus concentrations, a plaque reduction neutralization assays (PRNT), and a chemiluminescence assay that measures IgG binding to N and S proteins of SARS-CoV-2. Our results indicated that a microneutralization assay using 100 TCID50/mL provides comparable results to PRNT and allows for high throughput testing.