CD79A and COVID-19: Third, overall both IgA and IgG/IgA-FCI returned more positive results overall than Roche ECLIA and Diasorin CLIA; However, this ultimately depended upon the time frame of serum collection after the onset of COVID-19 symptoms; in this sense FCI yielded more positive results than the other two immunoassays in early sera (drawn within 15 days after the onset of symptoms, whereas the Roche assay did so in sera collected afterwards.