Antibody dynamics to SARS-CoV-2 in asymptomatic COVID-19 infections

Background

The missing asymptomatic COVID-19 infections have been overlooked because of the imperfect sensitivity of the nucleic acid testing (NAT). Globally understanding the humoral immunity in asymptomatic carriers will provide scientific knowledge for developing serological tests, improving early identification, and implementing more rational control strategies against the pandemic.

Measure

Utilizing both NAT and commercial kits for serum IgM and IgG antibodies, we extensively screened 11 766 epidemiologically suspected individuals on enrollment and 63 asymptomatic individuals were detected and recruited. Sixty-three healthy individuals and 51 mild patients without any preexisting conditions were set as controls. Serum IgM and IgG profiles were further probed using a SARS-CoV-2 proteome microarray, and neutralizing antibody was detected by a pseudotyped virus neutralization assay system. The dynamics of antibodies were analyzed with exposure time or symptoms onset.

Results

A combination test of NAT and serological testing for IgM antibody discovered 55.5% of the total of 63 asymptomatic infections, which significantly raises the detection sensitivity when compared with the NAT alone (19%). Serum proteome microarray analysis demonstrated that asymptomatics mainly produced IgM and IgG antibodies against S1 and N proteins out of 20 proteins of SARS-CoV-2. Different from strong and persistent N-specific antibodies, S1-specific IgM responses, which evolved in asymptomatic individuals as early as the seventh day after exposure, peaked on days from 17 days to 25 days, and then disappeared in two months, might be used as an early diagnostic biomarker. 11.8% (6/51) mild patients and 38.1% (24/63) asymptomatic individuals did not produce neutralizing antibody. In particular, neutralizing antibody in asymptomatics gradually vanished in two months.

Conclusion

Our findings might have important implications for the definition of asymptomatic COVID-19 infections, diagnosis, serological survey, public health, and immunization strategies.

     

Upper respiratory tract SARS-CoV-2 RNA loads in symptomatic and asymptomatic children and adults

ObjectivesStudies comparing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA load in the upper respiratory tract (URT) between children and adults—who either presented with coronavirus disease 2019 (COVID-19) or were asymptomatic—have yielded inconsistent results. Here, we conducted a retrospective, single-centre study to address this issue.Patients and methodsIncluded were 1184 consecutive subjects (256 children and 928 adults) testing positive for SARS-CoV-2 RNA in nasopharyngeal exudates (NPs); of these, 424 (121 children and 303 adults) had COVID-19 and 760 (135 children and 625 adults) were asymptomatic close contacts of COVID-19 patients. SARS-CoV-2 RNA testing was carried out using the TaqPath COVID-19 Combo Kit (Thermo Fisher Scientific, MS, USA). The AMPLIRUN® TOTAL SARS-CoV-2 RNA Control (Vircell SA, Granada, Spain) was used for estimating SARS-CoV-2 RNA loads (in copies/mL). SARS-CoV-2 RNA loads at the time of laboratory diagnosis (single specimen/patient) were used for comparison purposes.ResultsMedian initial SARS-CoV-2 RNA load was lower (p 0.094) in children (6.98 log₁₀ copies/mL, range 3.0–11.7) than in adults (7.14 log₁₀ copies/mL, range 2.2–13.4) with COVID-19. As for asymptomatic individuals, median SARS-CoV-2 RNA load was comparable (p 0.97) in children (6.20 log₁₀ copies/mL, range 1.8–11.6) and adults (6.48 log₁₀ copies/mL, range 1.9–11.8). Children with COVID-19 symptoms displayed SARS-CoV-2 RNA loads (6.98 log₁₀ copies/mL, range 3.0–11.7) comparable to those of their asymptomatic counterparts (6.20 log₁₀ copies/mL, range 1.8–11.6) (p 0.61). Meanwhile in adults, median SARS-CoV-2 RNA load was significantly higher in symptomatic (7.14 log₁₀ copies/mL, range 2.2–13.4) than in asymptomatic subjects (6.48 log₁₀ copies/mL, range 1.9–11.8) (p < 0.001). Overall, the observed URT SARS-CoV-2 RNA clearance rate was faster in children than in adults.ConclusionsBased on viral load data at the time of diagnosis, our results suggest that SARS-CoV-2-infected children, with or without COVID-19, may display NP viral loads of comparable magnitude to those found in their adult counterparts. However, children may have shorter viral shedding than adults.     

Clinical characteristics of asymptomatic and symptomatic patients with mild COVID-19

ObjectivesDetailed knowledge on the prevalence of asymptomatic cases of coronavirus disease 2019 (COVID-19) and the clinical characteristics of mild COVID-19 is essential for effective control of the COVID-19 pandemic. We determined the prevalence of asymptomatic cases of COVID-19 and characterized the symptoms of patients with mild COVID-19.MethodsStudy participants were recruited from a community facility designated for the isolation of patients without moderate-to-severe symptoms of COVID-19 in South Korea. The prevalence of asymptomatic patients at admission and the detailed symptoms of mild COVID-19 were evaluated through a questionnaire-based survey. Diagnosis of COVID-19 was confirmed by real-time RT-PCR.ResultsOf the 213 individuals with COVID-19, 41 (19.2%) were asymptomatic until admission. Among the remaining patients with mild COVID-19, the most common symptom was cough (40.1%; 69/172), followed by hyposmia (39.5%; 68/172) and sputum (39.5%; 68/172). Of the 68 individuals with hyposmia, 61 (90%) had accompanying symptoms such as hypogeusia, nasal congestion or rhinorrhoea. Fever (>37.5°C) was only observed in 20 (11.6%) individuals.ConclusionsAs much as one-fifth of individuals with COVID-19 remained asymptomatic from exposure to admission. Hyposmia was quite frequent among individuals with mild COVID-19, but fever was not. Social distancing should be strongly implemented to prevent disease transmission from asymptomatic individuals or those with mild and inconspicuous symptoms.     

A cross-sectional study of SARS-CoV-2 seroprevalence among asymptomatic healthcare workers in a tertiary healthcare centre: Assessing the impact of PPE guidelines

PurposeThe present study estimates the seroprevalence of SARS-COV-2 among asymptomatic HCWs and assess the impact of various categories of PPE.MethodsA cross-sectional study of asymptomatic HCW using different levels of PPE as per their risk profile was undertaken between 18th and 24th September 2020. Participant demographics and other relevant details including the levels of PPE used were recorded using a customized questionnaire. IgG antibodies against SARS-COV-2 were detected by chemiluminescence method & used as a surrogate marker for incomplete protection.ResultsOut of 1033 HCWs tested, overall SARS-COV-2 sero-prevalence was 25.8%. Univariate and multivariate analysis both demonstrated that ancillary workers including security staff (OR 5.589, P ​< ​0.001) and sanitary workers (OR 3.946, P ​< ​0.001) were at significantly higher risk of seropositivity irrespective of the PPE used as per guidelines, whereas doctors were at significantly lower risk of seropositivity (OR 0.307, P ​= ​0.005). Staff working in office areas was associated with reduced risk of seropositivity (OR 0.21, P ​= ​0.045).ConclusionsWe document high seroprevalence of SARS-COV-2 antibodies in asymptomatic HCWs. Doctors who are at the highest risk had the lowest seropositivity and seroprevalence among office staff having a risk level comparable to the general community was lower than that reported in general population, supporting the efficacy of PPE practices as per guidelines in these groups. In contrast, much higher rates of seropositivity were seen among ancillary workers despite the availability of adequate PPE. Active screening, proper PPE use as per guidelines, and regular infection control trainings including Covid appropriate behaviour are therefore essential to contain COVID-19 spread among HCW & preventing them to transfer infection to the patients.     

The role of chest CT in management of asymptomatic SARS-CoV-2 infections: A longitudinal multi-center study in Chongqing,China

Background: Multiple societies including the Fleischner Society do not recommend that CT is routinely used in asymptomatic SARS-CoV-2 infections; however, this advice is based on the limited evidence. In this study, we aim to confirm whether it is necessary to do CT scans in SARS-CoV-2 asymptomatic infections by summarizing the longitudinal chest CT and clinical features of asymptomatic SARS-CoV-2 infections.Methods: A total of 33 individuals (14 men and 19 women) with asymptomatic SARS-CoV-2 infections were retrospectively enrolled. Clinical data of CT positive and negative groups were compared. Longitudinal chest CT scans were reviewed for CT features and analyzed for temporal change.Results: Thirty-two (97%) individuals had positive results for first RT-PCR testing. For clinical data, only monocyte count showed a significant difference between CT positive and negative groups. For first chest CT, only eighteen (54.5%) individuals had abnormal manifestations, common CT features were GGO (88.9%) and consolidation (33.3%), the median number of segments involved was 3.0 (1.0-7.5). No case in CT negative group was abnormal on the follow-up CT. Three patterns of evolution throughout series of CT were observed in CT positive group, including gradual improvement (12, 66.7%), mismatch to improvement (3, 16.7%) and mild progression to improvement (3, 16.7%). On last CT scans, most cases had radiographic improvement but residual abnormalities. Significant differences were exhibited in density, long diameter, number of lung segments involved, and percentage of consolidation between the first and last CT scans. All cases had stable conditions and finally confirmed negative for SARS-CoV-2 RT-PCR tests without developing into severe pneumonia.Conclusion: Considering poor performance of CT in screening, stable conditions during followup, and good outcomes in asymptomatic SARS-CoV-2 infections, we confirm that it is unnecessary to do CT scans in asymptomatic SARS-CoV-2 infections.     

Comparison and application of different immunoassay methods for the detection of SARS-CoV-2

The detection data of IgM and IgG antibodies in 169 patients with coronavirus disease-2019 (COVID-19) were analyzed to evaluate differences in clinical performance between the colloidal gold method and chemiluminescence method. In this study, chemiluminescence detection of IgM antibody showed a positive conversion earlier (about 1-2 days earlier), positive conversion rates higher in different stages of disease, and a trend of declining positive rate later than colloidal gold method. For IgG antibody, the chemiluminescence method showed a positive conversion earlier and the positive rate climbing more quickly than the colloidal gold method. No obvious negative-converting tendency of IgG detection was observed within 35 days after the onset of disease. Although colloidal gold method is generally less sensitive than chemiluminescence method, it shows advantages of shorter turn-around time, more simple procedure, and no special equipment required. The two methodologies can be chosen according to different laboratory conditions. A reasonable understanding of the performance of reagents with different methodologies can help in clinical disease diagnosis effectively and assist in the diagnosis of the progression of COVID-19, for which the dynamic changes of antibody will provide reliable evidence.     

Risk of waning humoral responses after inactivated or subunit recombinant SARS-CoV-2 vaccination in patients with chronic diseases: Findings from a prospective observational study in China

Heterogeneity of antibody responses has been reported in SARS-CoV-2 vaccination recipients with underlying diseases. We investigated the impact of the presence of comorbidities on the humoral response to SARS-CoV-2 vaccination in patients with chronic disease (PWCD) and assessed the effect of the number of comorbidities on the humoral response to vaccination. In this study, neutralizing antibodies (NAbs) and IgG antibodies against the receptor-binding domain (RBD-IgG) were monitored following a full-course vaccination. In total, 1400 PWCD (82.7%, inactivated vaccines; 17.3%, subunit recombinant vaccine) and 245 healthy controls (65.7% inactivated vaccines, 34.3% subunit recombinant vaccine) vaccinated with inactivated or subunit recombinant SARS-CoV-2 vaccines, were included. The seroconversion and antibody levels of the NAbs and RBD-IgG were different in the PWCD group compared with those in the control group. Chronic hepatitis B (odds ratio [OR]: 0.65; 95% confidence interval [CI]: 0.46–0.93), cancer (OR: 0.65; 95% CI: 0.42–0.99), and diabetes (OR: 0.50; 95% CI: 0.28–0.89) were associated with lower seroconversion of NAbs. Chronic kidney disease (OR: 0.29; 95% CI: 0.11–0.76), cancer (OR: 0.38; 95% CI: 0.23–0.62), and diabetes (OR: 0.37; 95% CI: 0.20–0.69) were associated with lower seroconversion of RBD-IgG. Only the presence of autoimmune disease showed significantly lower NAbs and RBD-IgG titers. Patients with most types of chronic diseases showed similar responses to the controls, but humoral responses were still significantly associated with the presence of ≥2 coexisting diseases. Our study suggested that humoral responses following SARS-CoV-2 vaccination are impaired in patients with certain chronic diseases.     

Germline rare variants of lectin pathway genes predispose to asymptomatic SARS-CoV-2 infection in elderly individuals

PurposeEmerging evidence suggest that infection-dependent hyperactivation of complement system (CS) may worsen COVID-19 outcome. We investigated the role of predicted high impact rare variants — referred as qualifying variants (QVs) — of CS genes in predisposing asymptomatic COVID-19 in elderly individuals, known to be more susceptible to severe disease.MethodsExploiting exome sequencing data and 56 CS genes, we performed a gene-based collapsing test between 164 asymptomatic subjects (aged ≥60 years) and 56,885 European individuals from the Genome Aggregation Database. We replicated this test comparing the same asymptomatic individuals with 147 hospitalized patients with COVID-19.ResultsWe found an enrichment of QVs in 3 genes (MASP1, COLEC11, and COLEC10), which belong to the lectin pathway, in the asymptomatic cohort. Analyses of complement activity in serum showed decreased activity of lectin pathway in asymptomatic individuals with QVs. Finally, we found allelic variants associated with asymptomatic COVID-19 phenotype and with a decreased expression of MASP1, COLEC11, and COLEC10 in lung tissue.ConclusionThis study suggests that genetic rare variants can protect from severe COVID-19 by mitigating the activity of lectin pathway and prothrombin. The genetic data obtained through ES of 786 asymptomatic and 147 hospitalized individuals are publicly available at http://espocovid.ceinge.unina.it/     

Detectable SARS-CoV-2 viral RNA in feces of three children during recovery period of COVID-19 pneumonia

Coronavirus Disease 2019 (COVID-19) is a newly emerging infectious disease caused by a novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). After its first occurrence in Wuhan of China from December 2019, COVID-19 rapidly spread around the world. According to the World Health Organization statement on 13 March 2020, there had been over 132 500 confirmed cases globally. Nevertheless, the case reports of children are rare, which results in the lack of evidence for preventing and controlling of children's infection. Here, we report three cases of SARS-CoV-2 infected children diagnosed from 3 February to 17 February 2020 in Tianjin, China. All of these three cases experienced mild illness and recovered soon after the treatment, with the nucleic acid of throat swab turning negative within 14, 11, and 7 days after diagnosis, respectively. However, after been discharged, all three cases were tested SARS-CoV-2 positive in the stool samples within 10 days, in spite of their remained negative nucleic acid in throat swab specimens. Therefore, it is necessary to be aware of the possibility of fecal-oral transmission of SARS-CoV-2 infection, especially for children cases.