The kinetics of viral load and antibodiesto SARS-CoV-2

OBJECTIVES: To understand persistence of the virus in body fluids and immune response of 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 (rRT-PCR), serum antibodies of IgA, IgG and IgM by enzyme linked immunosorbent assay (ELISA), 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∼8w) and throat (6.9×106 vs 2.9×105 , p<0.05; 4∼5w), while comparable in sputum samples (5.5×106 vs 0.9×106 , p<0.05; 4∼5w). Viraemia was rarely detected (2.8%, n=1/35). We detected early seroconversion of IgA and IgG at 1st 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 3rd week illness onset. The levels of neutralizing antibodies correlated with IgG (rs =0.85, p<0.05; kappa=0.85) and IgA (rs =0.64, p<0.05; kappa=0.61) in severe, but not mild cases (IgG, rs =0.42, kappa=0.33; IgA, rs =0.32, kappa=0.22). No correlation with IgM in either severe (rs =0.17, kappa=0.06) or mild cases (rs =0.27, kappa=0.15) was found.

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