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.

Graphical abstract

Fig. 1

Kinetics of viral load in 35 COVID-19 cases. The copies of SARS like coronavirus 2 (SARS-CoV-2) RNA in nasopharyngeal swab (A), throat swab (B), sputum (C), faeces (D) and serum specimens (E) were estimated by means of real-time reverse-transcriptase polymerase chain reaction. The dashed curve draws with exponential growth model and indicates the dynamic tendency of viral load in variety body fluids. Each dot of viral load present as mean and standard deviation. Purple symbols denote severe cases, and cyan symbols denote mild cases.

Fig. 2

Kinetics of IgA (A), Ig M (B), Ig G (C) and neutralizing antibodies (D) to SARS-CoV-2 over time in 35 COVID-19 cases. The dashed curve draws with experiential growth model and indicates the dynamic tendency of antibodies. Each dot of ELISA presents as mean and standard deviation, and titres of neutralizing antibodies present geometric mean and standard deviation. Purple symbols denote severe cases, and cyan symbols denote mild cases.

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