Viral RNA Shedding And Antibody Kinetics Of SARS-CoV-2 Infections

BackgroundCoronavirus disease 2019(COVID-19),caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),has spread rapidly around the world,posing a major threat to human health and the economy.Currently,long-term data on viral shedding and the serum antibody responses in COVID-19 patients are still limited.Objectives1.Virus shedding and antibody kinetics in COVID-19 patients;2.Virus shedding and antibody kinetics in asymptomatic SARS-CoV-2 infections.MethodsDemographic information and clinical examination results were obtained from the electronic medical records.The RNA load of SARS-CoV-2 in throat swabs was measured by real-time fluorescence PCR using primers and probes targeting the ORF1Ab and N genes of SARS-CoV-2 to analyze the pattern of virus shedding.The total anti-SARS-CoV-2 antibody levels detected by chemiluminescence microparticle immunoassay and the anti-SARS-CoV-2 N protein IgM,anti-SARS-CoV-2 N protein IgG,anti-SARS-CoV-2 S protein RBD IgM and anti-SARS-CoV-2 S protein RBD IgG levels detected by enzyme-linked immunosorbent assay were used to analyze the antibody dynamics of different populations.All the data were statistically analyzed.Results1.Virus shedding and antibody kinetics in COVID-19 patients:According to the screening criteria,a total of 112 COVID-19 patients were included in this study with age ranging from 22 to 89 years old,including 62 males(55.36%)and 87 patients(77.7%)with mild symptoms.Fever was the most common symptom among them.The level of C-reactive protein in severe group(median 51.57 mg/L;IQR 23.99-113.50 mg/L)was significantly higher than that of the mild group(median 6.27 mg/L;IQR 1.45-22.62 mg/L;P<0.001).Peak viral loads in throat swabs were in most cases already detectable at the initial presentation of symptoms.The peak viral load in throat swabs of severe patients(median Ct value 31.48;IQR 24.03-36.64)was higher than that of mild patients(median CT value 36.39;IQR 31.62-37;P=0.002).Anti-SARS-CoV-2 N protein IgM reached the peak within 2 weeks after onset,and decreased to the detection limit 4-6 weeks after onset The level of anti-SARS-CoV-2 N protein IgM was higher in male,elderly and severe patients.The anti-SARS-CoV-2 S protein RBD IgM reached its peak within 2-4 weeks of onset,and the levels were higher in men and severe patients.The levels of anti-SARS-CoV-2 N protein IgG and anti-SARS-CoV-2 S protein RBD IgG were relatively stable within 2 weeks of illness onset.After 5-7 months of illness onset,the level of total antiSARS-CoV-2 antibodies decreased significantly compared with that in the acute stage in both mild and severe patients.The median percentage of decrease was 46.31%(IQR 5.37%-68.96%)in the mild group,and the median percentage of decrease was 46.02%(IQR 11.01%-65.75%)in the severe group.2.Virus shedding and antibody kinetics in asymptomatic SARS-CoV-2 infections:According to the screening criteria,a total of 18 asymptomatic patients with SARS-CoV-2 infection were enrolled in this study,with a median age of 38 years(IQR 23-55.75 years),and there were 7 males(38.89%).77.78%(14/18)of asymptomatic infected individuals had a viral shedding duration of less than 10 days.The level of total antibodies against SARS-CoV-2 in asymptomatic individuals was significantly lower than that of symptomatic patients,and the positive rate of anti-SARS-CoV-2 N protein IgG was significantly lower than that of symptomatic patients within 3 weeks after the data of diagnosis.The positive rate of anti-SARS-CoV-2 N protein IgM in asymptomatic patients was lower than that in symptomatic patients.ConclusionThe peak viral load and antibody levels of severe patients were higher than that of mild patients.Antibodies to SARS-CoV-2 last at least 6 months after onset.Lower levels of antibodies and delayed IgG seroconversion were observed in asymptomatic individuals,indicating that asymptomatic individuals had a weak immune response to SARS-COV-2 infection.