COVID-19 and humoral immune response in convalescent plasma donors in Pakistani cohort.

Abstract

Current COVID-19 pandemic has affected the entire globe. While there was no vaccine neither any specific treatment, investigational use of convalescent plasma has been explored in clinical trials. A prospective multicenter study of convalescent plasma was conducted. Donors were tested for total Anti-SARS-CoV-2 antibodies by electrochemiluminescence (ECLIA) and RT-PCR for COVID-19. Enzyme Linked Immunosorbent Assay (ELISA) was used to detect semi-quantitative and quantitative IgG anti-SARS-COV-2 antibodies. IgG Immunofluorescence-based lateral flow immunoassay (LFIA) was used to recheck seronegative donors. A total of 400 donors were enrolled. Twelve donors were SARS-CoV-2 positive by RT-PCR. Nine of 12 donors had developed SARS-CoV-2 IgG antibodies, while in 3 donors antibodies were not developed. A total of 70 donors (17.5%) were deferred due to seronegative status; 64 (16%) of them did not develop antibodies when plasma collection was planned. The IgG semiquantitative ELISA was positive in 282 and quantitative in 284 of 330 donors with a mean value of >1:160 and 44.10±39.22 IU/ml respectively. A total of 116 (29%) donors did not show IgG humoral response to COVID-19 even 28 days from the onset of illness. Subsequently, LFIA method was able to detect IgG antibodies in 20 of 48 (41.6%) seronegative donors and in 20 of 34 (58.8%) ECLIA positive ELISA negative donors. Viral RNA detection in recovered asymptomatic patients with concomitant IgG antibodies indicates recovery. Inability to detect antibodies by different testing kits may be due to their different antigenic targets or sensitivity. Significance of a positive COVID-19 RT-PCR in asymptomatic recovered patients is yet to be determined.