The kinetics of viral load and antibodies to SARS-CoV-2

Abstract

Objectives: The aim was to understand persistence of the virus in body fluids the and immune response of an infected host to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), an agent of coronavirus disease 2019 (COVID-19).

Methods: We determined the kinetics of viral load in several body fluids through real time reverse transcription polymerase chain reaction, serum antibodies of IgA, IgG and IgM by enzyme-linked immunosorbent assay and neutralizing antibodies by microneutralization assay in 35 COVID-19 cases from two hospitals in Guangdong, China.

Results: We found higher viral loads and prolonged shedding of virus RNA in severe cases of COVID-19 in nasopharyngeal (1.3 × 10⁶ vs 6.4 × 10⁴, p < 0.05; 7∼8 weeks) and throat (6.9 × 10⁶ vs 2.9 × 10⁵, p < 0.05; 4∼5 weeks), but similar in sputum samples (5.5 × 10⁶ vs 0.9 × 10⁶, p < 0.05; 4∼5 weeks). Viraemia was rarely detected (2.8%, n = 1/35). We detected early seroconversion of IgA and IgG at the first week after illness onset (day 5, 5.7%, n = 2/35). Neutralizing antibodies were produced in the second week, and observed in all 35 included cases after the third week illness onset. The levels of neutralizing antibodies correlated with IgG (r_s = 0.85, p < 0.05; kappa = 0.85) and IgA (r_s = 0.64, p < 0.05; kappa = 0.61) in severe, but not mild cases (IgG, r_s = 0.42, kappa = 0.33; IgA, r_s = 0.32, kappa = 0.22). No correlation with IgM in either severe (r_s = 0.17, kappa = 0.06) or mild cases (r_s = 0.27, kappa = 0.15) was found.

Discussion: We revealed a prolonged shedding of virus RNA in the upper respiratory tract, and evaluated the consistency of production of IgG, IgA, IgM and neutralizing antibodies in COVID-19 cases.

Keywords: COVID-19; IgA; IgG; IgM; Neutralizing antibodies; SARS-CoV-2; Viral load.