A possible dose-response equation: Viral load after plasma infusion in COVID-19 patients and anti-SARS-CoV-2 antibody titers in convalescent plasma.

BACKGROUND: Clinical trials of convalescent plasma therapy for coronavirus disease 2019 (COVID-19) are extensive, but the relationship between antibody titers, infused volume of plasma and virus clearance in patients remains unknown. This study proposed a possible estimating equation for clinical use of high antibody titer convalescent plasma. METHODS: A total of 38 patients were recruited in the Guanggu District Maternal and Child Health Hospital of Hubei Province from March 1 to 30, 2020. COVID-19 convalescent plasma was collected and high-titer (≥1:640) anti-S-RBD units used. The SARS-CoV-2 nucleic acid viral load was measured 24 h before and 72 h after convalescent plasma infusion. RESULTS: Convalescent plasma therapy was associated with reduced viral load in patients with moderate and severe severity. The viral negative rate at 72 h was 65.8%. The disappearance of viral nucleic acid in study patients was positively correlated with infuscate antibody titer and volume (r = 0.3375, p = 0.04). A possible estimation equation was as follows: Log10 (Reduction in viral load) = 0.18 + 0.001 × (Log2 S-RBD antibody titer × Plasma infusion volume) (r = 0.424, p = 0.009). In a single case, the viral nucleic acid persisted 14 days after the fourth plasma infusion. CONCLUSIONS: This study proposes a potential dose-response equation that adds a convenient way to estimate the dose of convalescent plasma product. It is beneficial to facilitate the rational allocation of plasma with high antibody titers and provide an individualised use strategy for convalescent plasma therapy.