Early Viral Clearance and Antibody Kinetics of COVID-19 Among Asymptomatic Carriers

Abstract

Asymptomatic carriers contribute to the spread of Coronavirus Disease 2019 (COVID-19), but their clinical characteristics, viral kinetics, and antibody responses remain unclear. A total of 56 COVID-19 patients without symptoms at admission and 19 age-matched symptomatic patients were enrolled. RNA of SARS-CoV-2 was tested using transcriptase quantitative PCR, and the total antibodies (Ab), IgG, IgA, and IgM against the SARS-CoV-2 were tested using Chemiluminescence Microparticle Immuno Assay. Among 56 patients without symptoms at admission, 33 cases displayed symptoms and 23 remained asymptomatic throughout the follow-up period. 43.8% of the asymptomatic carriers were children and none of the asymptomatic cases had recognizable changes in C-reactive protein or interleukin-6, except one 64-year-old patient. The initial threshold cycle value of nasopharyngeal SARS-CoV-2 in asymptomatic carriers was similar to that in pre-symptomatic and symptomatic patients, but the positive viral nucleic acid detection period of asymptomatic carriers (9.63 days) was shorter than pre-symptomatic patients (13.6 days). There were no obvious differences in the seropositive conversion rate of total Ab, IgG, and IgA among the three groups, though the rates of IgM varied largely. The average peak IgG and IgM COI of asymptomatic cases was 3.5 and 0.8, respectively, which is also lower than those in symptomatic patients with peaked IgG and IgM COI of 4.5 and 2.4 (p < 0.05). Young COVID-19 patients seem to be asymptomatic cases with early clearance of SARS-CoV-2 and low levels of IgM generation but high total Ab, IgG, and IgA. Our findings provide empirical information for viral clearance and antibody kinetics of asymptomatic COVID-19 patients.

Keywords: COVID-19; SARS-CoV-2; antibody; asymptomatic; viral clearance.

Figure 1

Participant profile. The figure depicts the study design and general inclusion criteria of the study.

Figure 2

The kinetics of SARS-CoV-2 RNA in nasopharyngeal and anal samples. The threshold cycle (Ct) of nasopharyngeal (A) and anal (B) samples from patients with positive SARS-CoV-2 RNA test. Patients with totally negative results were not enrolled. Each point represents a sample, curves represent best fit line. Fit Spline/LOWESS of XY analyses with default ones was used for the fitted curve. Negative results are denoted with a Ct of 40.

Figure 3

The seroconversion rate of antibodies in the plasma of different patients. Dynamic seropositive rate of total Ab (A), IgG (B), IgM (C), and IgA (D) of different patients at different stage. Patients were divided into four groups: 1–7 days, 8–14 days, 15–30 days, and 31–65 days.

Figure 4

Dynamics of SARS-CoV-2 specific antibodies. The levels of total Ab (A), IgG (B), IgM (C), and IgA (D) of different patients after onset. The relative antibody level was estimated using log₂ (COI). Each dot represents a sample, curves represent the best fit line. Fit Spline/LOWESS of XY analyses with default ones was used for the fitted curve. Patients with totally negative antibodies or only one sample were excluded. Negative results are shown below the dotted horizontal lines.