Validation of a commercially available SARS-CoV-2 serological immunoassay

Rapid antibody diagnostics for SARS-CoV-2 adaptive immune response

The emergence of a pandemic scale respiratory illness (COVID-19: coronavirus disease 2019) and the lack of the world's readiness to prevent its spread resulted in an unprecedented rise of biomedical diagnostic industries, as they took lead to provide efficient diagnostic solutions for COVID-19. However, these circumstances also led to numerous emergency use authorizations without appropriate evaluation that compromised standards, which could result in a larger than usual number of false-positive or false-negative results, leading to unwanted ambiguity in already confusing realities of the pandemic-hit closures of the world economy. This review is aimed at comparing the claimed or reported clinical sensitivity and clinical specificity of commercially available rapid antibody diagnostics with independently evaluated clinical performance results of the tests. Thereby, we not only present the types of modern antibody diagnostics and their working principles but summarize their experimental evaluations and observed clinical efficiencies to highlight the research, development, and commercialization issues with future challenges. Still, it must be emphasized that the serological or antibody tests do not serve the purpose of early diagnosis but are more suitable for epidemiology and screening populaces with an active immune response, recognizing convalescent plasma donors, and determining vaccine efficacy.

Vulnerable patients forgo health care during the first wave of the Covid-19 pandemic

During the first wave of the Covid-19 pandemic, access to health care was limited, and patients encountered important delays for scheduled appointments and care. Empirical data relying on patients' reports of forgoing health care are scarce. This study investigated Covid-19-related self-reports of forgoing health care in a sample of vulnerable outpatients in Geneva, Switzerland. We collected data from 1167 adult outpatients, including clinically vulnerable patients (with chronic diseases), geriatric patients (involved in a health care network for people aged 60 or older), and socially vulnerable patients (involved in a migrant health program or a mobile outpatient community care center) in June 2020. Data on sociodemographic factors, forgoing health care, and anti-SARS-CoV-2 antibodies were collected. Of the patients, 38.5% reported forgoing health care. Forgoing health care was more frequent for younger patients, women, patients with a low level of education, and patients with a chronic disease (p < .001). There was no significant association between the presence of anti-SARS-CoV-2 antibodies and forgoing health care (p = .983). As the decrease in routine management of patients might have important and unpredictable adverse health consequences, avoiding delayed health care is crucial.

Performance evaluation of the Roche Elecsys Anti-SARS-CoV-2 S immunoassay

The Elecsys® Anti-SARS-CoV-2 S immunoassay (Roche Diagnostics International Ltd, Rotkreuz, Switzerland) has been developed for the detection of antibodies to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein. We evaluated the assay performance using samples from seven sites in Germany, Austria, and Switzerland. For specificity and sensitivity analyses, 7880 presumed negative pre-pandemic samples and 827 SARS-CoV-2 PCR-confirmed single or sequential samples from 272 different patients were tested, respectively. The overall specificity and sensitivity (≥14 days post-PCR) for the Elecsys Anti-SARS-CoV-2 S immunoassay were 99.95% (95% confidence interval [CI]: 99.87–99.99; 7876/7880) and 97.92% (95% CI: 95.21–99.32; 235/240), respectively. The Elecsys Anti-SARS-CoV-2 S immunoassay had significantly higher specificity compared with the LIAISON® SARS-CoV-2 S1/S2 IgG (99.95% [2032/2033] vs 98.82% [2009/2033]), ADVIA Centaur® SARS-CoV-2 Total (100% [928/928] vs 86.96% [807/928]), ARCHITECT SARS-CoV-2 IgG (99.97% [2931/2932] vs 99.69% [2923/2932]), iFlash-SARS-CoV-2 IgM (100.00% [928/928] vs 99.57% [924/928]), and EUROIMMUN Anti-SARS-CoV-2 IgG (100.00% [903/903] vs 97.45% [880/903]) and IgA (100.00% [895/895] vs 95.75% [857/895]) assays. The Elecsys Anti-SARS-CoV-2 S immunoassay had significantly higher sensitivity (≥14 days post-PCR) compared with the ARCHITECT SARS-CoV-2 IgG (98.70% [76/77] vs 87.01% [67/77]), iFlash-SARS-CoV-2 IgG (100.00% [76/76] vs 93.42% [71/76]) and IgM (100.00% [76/76] vs 35.53% [27/76]), and EUROIMMUN Anti-SARS-CoV-2 IgG (98.26% [113/115] vs 93.91% [108/115]) assays. Therefore, the Elecsys Anti-SARS-CoV-2 S assay demonstrated a reliable performance across various sample populations for the detection of anti-S antibodies.

Evaluation of Antibody Responses to COVID-19 Vaccines among Solid Tumor and Hematologic Patients

Simple Summary

Vaccination is the primary public health strategy to cope with the COVID-19 pandemic. Although solid tumor and hematologic patients are at higher risk of serious COVID-19-related complications and mortality, data on immune responses to COVID-19 vaccines in this patient cohort are particularly scarce. Our results show that antibody titers against the SARS-CoV-2 spike protein are significantly higher in solid tumor vs. hematologic patients. While SARS-CoV-2 antibody titers were equal among sexes, an age-dependent decrease could be observed. Of note, our studies additionally show that complete vaccination represents a valuable predictor for high anti-SARS-CoV-2 antibody responses in solid tumor and hematologic patients. Our findings aim to support future vaccination strategies in these highly vulnerable patients, including vaccination booster programs and alternative protective approaches.

Abstract

Vaccination is the primary public health strategy to cope with the COVID-19 pandemic. Although solid tumor and hematologic patients are at higher risk of serious COVID-19-related complications, data on immune responses to COVID-19 vaccines in this patient cohort are particularly scarce. The present study, therefore, aimed at the standardized determination of anti-SARS-CoV-2 spike protein antibody titers among non-vaccinated versus vaccinated solid tumor and hematologic patients who are under clinical observation or under treatment at the University Hospital Krems. Standardized anti-SARS-CoV-2 S antibody titers of a total of 441 patients were retrospectively analyzed. Our results show that antibody titers against the SARS-CoV-2 spike protein are significantly higher in solid tumor versus hematologic patients. While SARS-CoV-2 antibody titers were equal among sexes, an age-dependent decrease was observed. Of note, our studies additionally show that complete vaccination represents a valuable predictor for high anti-SARS-CoV-2 antibody responses in solid tumor and hematologic patients. In summary, to date, this is one of the largest studies to comprehensively evaluate the impact of various COVID-19 vaccines on anti-SARS-CoV-2 S antibody production in solid tumor and hematologic patients. Our findings aim to support future vaccination strategies in these highly vulnerable patients, including vaccination booster programs and alternative protective approaches.

Immunogenicity and reactogenicity of BNT162b2 booster in ChAdOx1-S-primed participants (CombiVacS): a multicentre, open-label, randomised, controlled, phase 2 trial

BACKGROUND

To date, no immunological data on COVID-19 heterologous vaccination schedules in humans have been reported. We assessed the immunogenicity and reactogenicity of BNT162b2 (Comirnaty, BioNTech, Mainz, Germany) administered as second dose in participants primed with ChAdOx1-S (Vaxzevria, AstraZeneca, Oxford, UK).

METHODS

We did a phase 2, open-label, randomised, controlled trial on adults aged 18-60 years, vaccinated with a single dose of ChAdOx1-S 8-12 weeks before screening, and no history of SARS-CoV-2 infection. Participants were randomly assigned (2:1) to receive either BNT162b2 (0·3 mL) via a single intramuscular injection (intervention group) or continue observation (control group). The primary outcome was 14-day immunogenicity, measured by immunoassays for SARS-CoV-2 trimeric spike protein and receptor binding domain (RBD). Antibody functionality was assessed using a pseudovirus neutralisation assay, and cellular immune response using an interferon-γ immunoassay. The safety outcome was 7-day reactogenicity, measured as solicited local and systemic adverse events. The primary analysis included all participants who received at least one dose of BNT162b2 and who had at least one efficacy evaluation after baseline. The safety analysis included all participants who received BNT162b2. This study is registered with EudraCT (2021-001978-37) and ClinicalTrials.gov (NCT04860739), and is ongoing.

FINDINGS

Between April 24 and 30, 2021, 676 individuals were enrolled and randomly assigned to either the intervention group (n=450) or control group (n=226) at five university hospitals in Spain (mean age 44 years [SD 9]; 382 [57%] women and 294 [43%] men). 663 (98%) participants (n=441 intervention, n=222 control) completed the study up to day 14. In the intervention group, geometric mean titres of RBD antibodies increased from 71·46 BAU/mL (95% CI 59·84-85·33) at baseline to 7756·68 BAU/mL (7371·53-8161·96) at day 14 (p<0·0001). IgG against trimeric spike protein increased from 98·40 BAU/mL (95% CI 85·69-112·99) to 3684·87 BAU/mL (3429·87-3958·83). The interventional:control ratio was 77·69 (95% CI 59·57-101·32) for RBD protein and 36·41 (29·31-45·23) for trimeric spike protein IgG. Reactions were mild (n=1210 [68%]) or moderate (n=530 [30%]), with injection site pain (n=395 [88%]), induration (n=159 [35%]), headache (n=199 [44%]), and myalgia (n=194 [43%]) the most commonly reported adverse events. No serious adverse events were reported.

INTERPRETATION

BNT162b2 given as a second dose in individuals prime vaccinated with ChAdOx1-S induced a robust immune response, with an acceptable and manageable reactogenicity profile.

FUNDING

Instituto de Salud Carlos III.

TRANSLATIONS

For the French and Spanish translations of the abstract see Supplementary Materials section.

Case-Control Study of Individuals with Discrepant Nucleocapsid and Spike Protein SARS-CoV-2 IgG Results

BACKGROUND

Laboratory-based methods for SARS-CoV-2 antibody detection vary widely in performance. However, there are limited prospectively-collected data on assay performance, and minimal clinical information to guide interpretation of discrepant results.

METHODS

Over a 2-week period, 1080 consecutive plasma samples submitted for clinical SARS-CoV-2 IgG testing were tested in parallel for anti-nucleocapsid IgG (anti-N, Abbott) and anti-spike IgG (anti-S1, EUROIMMUN). Chart review was conducted for samples testing positive or borderline on either assay, and for an age/sex-matched cohort of samples negative by both assays. CDC surveillance case definitions were used to determine clinical sensitivity/specificity and conduct receiver operating characteristics curve analysis.

RESULTS

There were 52 samples positive by both methods, 2 positive for anti-N only, 34 positive for anti-S1 only, and 27 borderline for anti-S1. Of the 34 individuals positive for anti-S1 alone, 8 (24%) had confirmed COVID-19. No anti-S1 borderline cases were positive for anti-N or had confirmed/probable COVID-19. The anti-N assay was less sensitive (84.2% [95% CI 72.1-92.5%] vs 94.7% [95% CI 85.4-98.9%]) but more specific (99.2% [95% CI 95.5-100%] vs 86.9% [95% CI 79.6-92.3%]) than anti-S1. Abbott anti-N sensitivity could be improved to 96.5% with minimal effect on specificity if the index threshold was lowered from 1.4 to 0.6.

CONCLUSION

Real-world concordance between different serologic assays may be lower than previously described in retrospective studies. These findings have implications for the interpretation of SARS-CoV-2 IgG results, especially with the advent of spike antigen-targeted vaccination, as a subset of patients with true infection are anti-N negative and anti-S1 positive.

Antibody response to SARS-CoV-2 vaccination is extremely vivacious in subjects with previous SARS-CoV-2 infection

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic calls for rapid actions, now principally oriented to a world-wide vaccination campaign. In this study we verified if, in individuals with a previous SARS-CoV-2 infection, a single dose of messenger RNA (mRNA) vaccine would be immunologically equivalent to a full vaccine schedule in naïve individuals. Health care workers (184) with a previous SARS-CoV-2 infection were sampled soon before the second dose of vaccine and between 7 and 10 days after the second dose, the last sampling time was applied to SARS-CoV-2 naïve individuals, too. Antibodies against SARS-CoV-2 were measured using Elecsys Anti-SARS-CoV-2 S immunoassay. The study was powered for non-inferiority. We used non parametric tests and Pearson correlation test to perform inferential analysis. After a single vaccine injection, the median titer of specific antibodies in individuals with previous coronavirus disease 2019 was 30.527 U/ml (interquartile range [IQR]: 19.992-39.288) and in subjects with previous SARS-CoV-2 asymptomatic infection was 19.367.5 U/ml (IQR: 14.688-31.353) (p = .032). Both results were far above the median titer in naïve individuals after a full vaccination schedule: 1974.5 U/ml (IQR: 895-3455) (p < .0001). Adverse events after vaccine injection were more frequent after the second dose of vaccine (mean: 0.95; 95% confidence interval [CI]: 0.75-1.14 vs. mean: 1.91; 95% CI: 1.63-2.19) (p < .0001) and in exposed compared to naïve (mean: 1.63; 95% CI: 1.28-1.98 vs. mean: 2.35; 95% CI: 1.87-2.82) (p = .015). In SARS-CoV-2 naturally infected individuals a single mRNA vaccine dose seems sufficient to reach immunity. Modifying current dosing schedules would speed-up vaccination campaigns.

SARS-CoV-2 outbreak in a synagogue community: longevity and strength of anti-SARS-CoV-2 IgG responses

Severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) pandemic is still ongoing along with the global vaccination efforts against it. Here, we aimed to understand the longevity and strength of anti-SARS-CoV-2 IgG responses in a small community (n = 283) six months following local SARS-COV-2 outbreak in March 2020. Three serological assays were compared and neutralisation capability was also determined. Overall 16.6% (47/283) of the participants were seropositive and 89.4% (42/47) of the IgG positives had neutralising antibodies. Most of the symptomatic individuals confirmed as polymerase chain reaction (PCR) positive during the outbreak were seropositive (30/32, 93.8%) and 33.3% of the individuals who quarantined with a PCR confirmed patient had antibodies. Serological assays comparison revealed that Architect (Abbott) targeting the N protein LIASON^® (DiaSorin) targeting the S protein and enzyme-linked immunosorbent assay (ELISA) targeting receptor binding domain detected 9.5% (27/283), 17.3% (49/283) and 17% (48/283), respectively, as IgG positives. The latter two assays highly agreed (kappa = 0.89) between each other. In addition, 95%, (19/20, by ELISA) and 90.9% (20/22, with LIASON) and only 71.4% (15/21, by Architect) of individuals that were seropositive in May 2020 were found positive also in September. The unexpected low rate of overall immunity indicates the absence of un-noticed, asymptomatic infections. Lack of overall high correlation between the assays is attributed mainly to target-mediated antibody responses and suggests that using a single serological assay may be misleading.

The prevalence of HEV among non-A-C hepatitis in Qatar and efficiency of serological markers for the diagnosis of hepatitis E

BACKGROUND

The rapid growth of Qatar in the last two decades has attracted a large influx of immigrant workers who mostly come from HEV-hyperendemic countries. Thus, we aim to investigate the prevalence of HEV among acute non-A-C hepatitis patients in Qatar; and to evaluate the performance of four dominant commercial serological assays for HEV diagnosis.

METHODS

259 patients with non-A-C hepatitis were tested using the Wantai HEV-IgM, HEV-IgG, HEV-Ag ELISA kits, and the MP Biomedical HEV-Total Ab ELISA kit. ALT levels were tested and HEV RNA (viral loads) was performed using Taqman AmpliCube HEV RT-PCR kit (Mikrogen, Neuried, Germany). The performance of each kit was assessed according to the RT-PCR results.

RESULTS

HEV-RNA was detected in 23.1% of the samples. Most of these HEV-RNA-positive cases belonged to non-Qatari residents from the Indian subcontinent; India, Pakistan, etc. HEV-Ag, HEV-IgM, HEV-IgG, HEV-Total Ab were detected in 5.56%, 8.65%, 32.1%, and 34.2% of all tested samples, respectively. Elevated ALT levels were highly correlated with the HEV-Ag, HEV-IgM, HEV-RNA but not with the HEV-IgG and HEV-Total Ab. Although HEV-Ag was very specific (100%), yet its sensitivity was poor (36.7%). HEV-IgM demonstrated the best second marker for diagnosis of acute HEV after RT-PCR as jugged by the overall performance parameters: specificity (96.2%), sensitivity (71.4%), PPV (83.3%), NPP (92.7%), agreement with RT-PCR (91.0%), and Kappa-value (0.71).

CONCLUSION

Our study demonstrated a high prevalence of HEV virus in Qatar, mostly among immigrants from the Indian subcontinent. The HEV-IgM represents the best marker for detecting the acute HEV infection, where RT-PCR cannot be performed.

Insights into household transmission of SARS-CoV-2 from a population-based serological survey

Understanding the risk of infection from household- and community-exposures and the transmissibility of asymptomatic infections is critical to SARS-CoV-2 control. Limited previous evidence is based primarily on virologic testing, which disproportionately misses mild and asymptomatic infections. Serologic measures are more likely to capture all previously infected individuals. We apply household transmission models to data from a cross-sectional, household-based population serosurvey of 4,534 people ≥5 years from 2,267 households enrolled April-June 2020 in Geneva, Switzerland. We found that the risk of infection from exposure to a single infected household member aged ≥5 years (17.3%,13.7-21.7) was more than three-times that of extra-household exposures over the first pandemic wave (5.1%,4.5-5.8). Young children had a lower risk of infection from household members. Working-age adults had the highest extra-household infection risk. Seropositive asymptomatic household members had 69.4% lower odds (95%CrI,31.8-88.8%) of infecting another household member compared to those reporting symptoms, accounting for 14.5% (95%CrI, 7.2-22.7%) of all household infections.

Large variation in anti-SARS-CoV-2 antibody prevalence among essential workers in Geneva, Switzerland

Limited data exist on SARS-CoV-2 infection rates across sectors and occupations, hindering our ability to make rational policy, including vaccination prioritization, to protect workers and limit SARS-CoV-2 spread. Here, we present results from our SEROCoV-WORK + study, a serosurvey of workers recruited after the first wave of the COVID-19 pandemic in Geneva, Switzerland. We tested workers (May 18-September 18, 2020) from 16 sectors and 32 occupations for anti-SARS-CoV-2 IgG antibodies. Of 10,513 participants, 1026 (9.8%) tested positive. The seropositivity rate ranged from 4.2% in the media sector to 14.3% in the nursing home sector. We found considerable within-sector variability: nursing home (0%-31.4%), homecare (3.9%-12.6%), healthcare (0%-23.5%), public administration (2.6%-24.6%), and public security (0%-16.7%). Seropositivity rates also varied across occupations, from 15.0% among kitchen staff and 14.4% among nurses, to 5.4% among domestic care workers and 2.8% among journalists. Our findings show that seropositivity rates varied widely across sectors, between facilities within sectors, and across occupations, reflecting a higher exposure in certain sectors and occupations.

Prevalence of SARS-CoV-2 Infection in Children and Their Parents in Southwest Germany

Importance

School and daycare closures were enforced as measures to confine the novel coronavirus disease 2019 (COVID-19) pandemic, based on the assumption that young children may play a key role in severe acute respiratory coronavirus 2 (SARS-CoV-2) spread. Given the grave consequences of contact restrictions for children, a better understanding of their contribution to the COVID-19 pandemic is of great importance.

Objective

To describe the rate of SARS-CoV-2 infections and the seroprevalence of SARS-CoV-2 antibodies in children aged 1 to 10 years, compared with a corresponding parent of each child, in a population-based sample.

Design, Setting, and Participants

This large-scale, multicenter, cross-sectional investigation (the COVID-19 BaWü study) enrolled children aged 1 to 10 years and a corresponding parent between April 22 and May 15, 2020, in southwest Germany.

Exposures

Potential exposure to SARS-CoV-2.

Main Outcomes and Measures

The main outcomes were infection and seroprevalence of SARS-CoV-2. Participants were tested for SARS-CoV-2 RNA from nasopharyngeal swabs by reverse transcription-polymerase chain reaction and SARS-CoV-2 specific IgG antibodies in serum by enzyme-linked immunosorbent assays and immunofluorescence tests. Discordant results were clarified by electrochemiluminescence immunoassays, a second enzyme-linked immunosorbent assay, or an in-house Luminex-based assay.

Results

This study included 4964 participants: 2482 children (median age, 6 [range, 1-10] years; 1265 boys [51.0%]) and 2482 parents (median age, 40 [range, 23-66] years; 615 men [24.8%]). Two participants (0.04%) tested positive for SARS-CoV-2 RNA. The estimated SARS-CoV-2 seroprevalence was low in parents (1.8% [95% CI, 1.2-2.4%]) and 3-fold lower in children (0.6% [95% CI, 0.3-1.0%]). Among 56 families with at least 1 child or parent with seropositivity, the combination of a parent with seropositivity and a corresponding child with seronegativity was 4.3 (95% CI, 1.19-15.52) times higher than the combination of a parent who was seronegative and a corresponding child with seropositivity. We observed virus-neutralizing activity for 66 of 70 IgG-positive serum samples (94.3%).

Conclusions and Relevance

In this cross-sectional study, the spread of SARS-CoV-2 infection during a period of lockdown in southwest Germany was particularly low in children aged 1 to 10 years. Accordingly, it is unlikely that children have boosted the pandemic. This SARS-CoV-2 prevalence study, which appears to be the largest focusing on children, is instructive for how ad hoc mass testing provides the basis for rational political decision-making in a pandemic.

The Beauty of Simplicity: Delayed-Type Hypersensitivity Reaction to Measure Cellular Immune Responses in RNA-SARS-Cov-2 Vaccinated Individuals

Background: Monitoring cellular immune responses elicited in vaccinated individuals is highly complicated. Methods: 28 individuals participated during the vaccination process with 12 BNT162b2 mRNA (Pfizer) vaccine. Specific anti-RBD IgG using a classic ELISA was performed in days 10 and 20 (after one dose of the vaccine) and on day 35 (after two vaccine doses) in serum samples of all participants. In parallel, DTH (delayed-type hypersensitivity) Skin Test using S protein was performed before (11/28) and after two doses (28/28) of the vaccine. Results: 6/28 individuals were considered positive for the specific anti-RBD IgG positive at day 10, whereas all 28 individuals were positive at day 20. Moreover, 28/28 individuals increased the OD ratios at day 36 (2 doses). DTH cutaneous test was performed on 11/28 participants at day 20 (1 dose) showing 8/11 a positive reaction at 12 h. DTH of all participants was performed on day 36 (2 doses), showing 28/28 positive reactions at 12 h. Conclusion: This report describes the first publication of the results obtained using an in vivo method, the classical DTH response to the Spike protein to assess T-cell immune responses in vaccinated individuals. This affordable and simple test would help to answer basic immunogenicity questions on large-scale population vaccine studies.

Risk of reinfection after seroconversion to SARS-CoV-2: A population-based propensity-score matched cohort study

Background

Serological assays detecting anti-SARS-CoV-2 antibodies are being widely deployed in studies and clinical practice. However, the duration and effectiveness of the protection conferred by the immune response remains to be assessed in population-based samples. To estimate the incidence of newly acquired SARS-CoV-2 infections in seropositive individuals as compared to seronegative controls we conducted a retrospective longitudinal matched study.

Methods

A seroprevalence survey including a representative sample of the population was conducted in Geneva, Switzerland between April and June 2020, immediately after the first pandemic wave. Seropositive participants were matched one-to-two to seronegative controls, using a propensity-score including age, gender, immunodeficiency, BMI, smoking status and education level. Each individual was linked to a state-registry of SARS-CoV-2 infections. Our primary outcome was confirmed infections occurring from serological status assessment to the end of the second pandemic wave (January 2021).

Results

Among 8344 serosurvey participants, 498 seropositive individuals were selected and matched with 996 seronegative controls. After a mean follow-up of 35.6 (SD 3.2) weeks, 7 out of 498 (1.4%) seropositive subjects had a positive SARS-CoV-2 test, of whom 5 (1.0%) were classified as reinfections. In contrast, the infection rate was higher in seronegative individuals (15.5%, 154/996) during a similar follow-up period (mean 34.7 [SD 3.2] weeks), corresponding to a 94% (95%CI 86% to 98%, P<0.001) reduction in the hazard of having a positive SARS-CoV-2 test for seropositives.

Conclusions

Seroconversion after SARS-CoV-2 infection confers protection against reinfection lasting at least 8 months. These findings could help global health authorities establishing priority for vaccine allocation.

Clinical Utility of Biosensing Platforms for Confirmation of SARS-CoV-2 Infection

Despite collaborative efforts from all countries, coronavirus disease 2019 (COVID-19) pandemic has been continuing to spread globally, forcing the world into social distancing period, making a special challenge for public healthcare system. Before vaccine widely available, the best approach to manage severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is to achieve highest diagnostic accuracy by improving biosensor efficacy. For SARS-CoV-2 diagnostics, intensive attempts have been made by many scientists to ameliorate the drawback of current biosensors of SARS-CoV-2 in clinical diagnosis to offer benefits related to platform proposal, systematic analytical methods, system combination, and miniaturization. This review assesses ongoing research efforts aimed at developing integrated diagnostic tools to detect RNA viruses and their biomarkers for clinical diagnostics of SARS-CoV-2 infection and further highlights promising technology for SARS-CoV-2 specific diagnosis. The comparisons of SARS-CoV-2 biomarkers as well as their applicable biosensors in the field of clinical diagnosis were summarized to give scientists an advantage to develop superior diagnostic platforms. Furthermore, this review describes the prospects for this rapidly growing field of diagnostic research, raising further interest in analytical technology and strategic plan for future pandemics.

SARS-CoV-2 antibody immunoassays in serial samples reveal earlier seroconversion in acutely ill COVID-19 patients developing ARDS

OBJECTIVES

During the COVID-19 pandemic, SARS-CoV-2 antibody testing has been suggested for (1) screening populations for disease prevalence, (2) diagnostics, and (3) guiding therapeutic applications. Here, we conducted a detailed clinical evaluation of four Anti-SARS-CoV-2 immunoassays in samples from acutely ill COVID-19 patients and in two negative cohorts.

METHODS

443 serum specimens from serial sampling of 29 COVID-19 patients were used to determine clinical sensitivities. Patients were stratified for the presence of acute respiratory distress syndrome (ARDS). Individual serum specimens from a pre-COVID-19 cohort of 238 healthy subjects and from a PCR-negative clinical cohort of 257 patients were used to determine clinical specificities. All samples were measured side-by-side with the Anti-SARS-CoV-2-ELISA (IgG), Anti-SARS-CoV-2-ELISA (IgA) and Anti-SARS-CoV-2-NCP-ELISA (IgG) (Euroimmun AG, Lübeck, Germany) and the Elecsys Anti-SARS-CoV-2 ECLIA (Roche Diagnostics International, Rotkreuz, Switzerland).

RESULTS

Median seroconversion occurred earlier in ARDS patients (8-9 days) than in non-ARDS patients (11-17 days), except for EUR N-IgG. Rates of positivity and mean signal ratios in the ARDS group were significantly higher than in the non-ARDS group. Sensitivities between the four tested immunoassays were equivalent. In the set of negative samples, the specificity of the Anti-SARS-CoV-2-ELISA (IgA) was lower (93.9%) compared to all other assays (≥98.8%) and the specificity of Anti-SARS-CoV-2-NCP-ELISA (IgG) was lower (98.8%) than that of Elecsys Anti-SARS-CoV-2 (100%).

CONCLUSIONS

Serial sampling in COVID-19 patients revealed earlier seroconversion and higher signal ratios of SARS-CoV-2 antibodies as a potential risk marker for the development of ARDS, suggesting a utility for antibody testing in acutely diseased patients.

Review of Current COVID-19 Diagnostics and Opportunities for Further Development

Diagnostic testing plays a critical role in addressing the coronavirus disease 2019 (COVID-19) pandemic, caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Rapid and accurate diagnostic tests are imperative for identifying and managing infected individuals, contact tracing, epidemiologic characterization, and public health decision making. Laboratory testing may be performed based on symptomatic presentation or for screening of asymptomatic people. Confirmation of SARS-CoV-2 infection is typically by nucleic acid amplification tests (NAAT), which requires specialized equipment and training and may be particularly challenging in resource-limited settings. NAAT may give false-negative results due to timing of sample collection relative to infection, improper sampling of respiratory specimens, inadequate preservation of samples, and technical limitations; false-positives may occur due to technical errors, particularly contamination during the manual real-time polymerase chain reaction (RT-PCR) process. Thus, clinical presentation, contact history and contemporary phyloepidemiology must be considered when interpreting results. Several sample-to-answer platforms, including high-throughput systems and Point of Care (PoC) assays, have been developed to increase testing capacity and decrease technical errors. Alternatives to RT-PCR assay, such as other RNA detection methods and antigen tests may be appropriate for certain situations, such as resource-limited settings. While sequencing is important to monitor on-going evolution of the SARS-CoV-2 genome, antibody assays are useful for epidemiologic purposes. The ever-expanding assortment of tests, with varying clinical utility, performance requirements, and limitations, merits comparative evaluation. We herein provide a comprehensive review of currently available COVID-19 diagnostics, exploring their pros and cons as well as appropriate indications. Strategies to further optimize safety, speed, and ease of SARS-CoV-2 testing without compromising accuracy are suggested. Access to scalable diagnostic tools and continued technologic advances, including machine learning and smartphone integration, will facilitate control of the current pandemic as well as preparedness for the next one.

A high-throughput microfluidic nanoimmunoassay for detecting anti-SARS-CoV-2 antibodies in serum or ultralow-volume blood samples

Novel technologies are needed to facilitate large-scale detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific antibodies in human blood samples. Such technologies are essential to support seroprevalence studies and vaccine clinical trials, and to monitor quality and duration of immunity. We developed a microfluidic nanoimmunoassay (NIA) for the detection of anti-SARS-CoV-2 IgG antibodies in 1,024 samples per device. The method achieved a specificity of 100% and a sensitivity of 98% based on the analysis of 289 human serum samples. To eliminate the need for venipuncture, we developed low-cost, ultralow-volume whole blood sampling methods based on two commercial devices and repurposed a blood glucose test strip. The glucose test strip permits the collection, shipment, and analysis of 0.6 μL of whole blood easily obtainable from a simple finger prick. The NIA platform achieves high throughput, high sensitivity, and specificity based on the analysis of 289 human serum samples, and negligible reagent consumption. We furthermore demonstrate the possibility to combine NIA with decentralized and simple approaches to blood sample collection. We expect this technology to be applicable to current and future SARS-CoV-2 related serological studies and to protein biomarker analysis in general.

Diagnostic accuracy of serological tests and kinetics of severe acute respiratory syndrome coronavirus 2 antibody: A systematic review and meta-analysis

This study aimed to assess the diagnostic test accuracy (DTA) of severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) serological test methods and the kinetics of antibody positivity. Systematic review and meta-analysis were conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guideline. We included articles evaluating the diagnostic accuracy of serological tests and the kinetics of antibody positivity. MEDLINE through PubMed, Scopus, medRxiv and bioRxiv were sources of articles. Methodological qualities of included articles were appraised using QUADAS-2 while Metandi performs bivariate meta-analysis of DTA using a generalized linear mixed-model approach. Stata 14 and Review Manager 5.3 were used for data analysis. The summary sensitivity/specificity of chemiluminescence immunoassay (CLIA), enzyme-linked immunosorbent assay (ELISA) and lateral flow immunoassay (LFIA) were 92% (95% CI: 86%-95%)/99% (CI: 97%-99%), 86% (CI: 82%-89%)/99% (CI: 98%-100%) and 78% (CI: 71%-83%)/98% (95% CI: 96%-99%), respectively. Moreover, CLIA-based assays produced nearly 100% sensitivity within 11-15 days post-symptom onset (DPSO). Based on antibody type, the sensitivity of ELISA-total antibody, CLIA-IgM/G and CLIA-IgG gauged at 94%, 92% and 92%, respectively. The sensitivity of CLIA-RBD assay reached 96%, while LFIA-S demonstrated the lowest sensitivity, 71% (95% CI: 58%-80%). CLIA assays targeting antibodies against RBD considered the best DTA. The antibody positivity rate increased corresponding with DPSO, but there was some decrement when moving from acute phase to convalescent phase of infection. As immunoglobulin isotope-related DTA was heterogeneous, our data have insufficient evidence to recommend CLIA/ELISA for clinical decision-making, but likely to have comparative advantage over RT-qPCR in certain circumstances and geographic regions.

The real life performance of 7 automated anti-SARS-CoV-2 IgG and IgM/IgA immunoassays

OBJECTIVES

This study was aimed at providing some insights into the real-life performance of the commercial, clinically validated anti-SARS-CoV-2 antibody assays.

METHODS

The residual, anonymized samples from 97 patients referred for anti-SARS-CoV-2 antibodies testing were included in the study. The initial assessment was performed with the Euroimmun ELISAs, followed by the assays provided by: NovaTec, Snibe, Vircell, Roche, Abbott and DiaSorin. The analyses of the results were performed separately for the antibodies of the early (IgM/IgA) and late (IgG) immune response.

RESULTS

We observed a high variability of the results obtained with the investigated immunoassays. The fully concordant results were reported for only 57 out of 97 samples tested for IgG antibodies and for 34 out of 97 samples for IgM/IgA. The highest percentage of positive results was noted for the Euroimmun and Vircell ELISAs and the lowest for Novatec ELISAs.We proposed to distinguish true and false positive results based on the sum of positive results obtained with different methods. We arbitrarily considered reference positive samples reactive in at least half of the assays. The assay that proved to correlate the best with those reference results was the Roche electrochemiluminescence immunoassay.

CONCLUSIONS

The differences observed between immunoassays targeting the early phase antibodies were much more pronounced than between IgG assays, suggesting their lower value for clinical use. Our study also showed a high percentage of plausibly false (positive or negative) results obtained with ELISAs, which suggests their inferiority to the automated immunoassays.

Evaluation of High-Throughput SARS-CoV-2 Serological Assays in a Longitudinal Cohort of Patients with Mild COVID-19: Clinical Sensitivity, Specificity, and Association with Virus Neutralization Test

BACKGROUND

The association between SARS-CoV-2 commercial serological assays and virus neutralization test (VNT) has been poorly explored in mild patients with COVID-19.

METHODS

439 serum specimens were longitudinally collected from 76 healthcare workers with RT-PCR-confirmed COVID-19. The clinical sensitivity (determined weekly) of 9 commercial serological assays were evaluated. Clinical specificity was assessed using 69 pre-pandemic sera. Correlation, agreement, and concordance with the VNT were also assessed on a subset of 170 samples. Area under the ROC curve (AUC) was estimated at 2 neutralizing antibody titers.

RESULTS

The Wantai Total Ab assay targeting the receptor binding domain (RBD) within the S protein presented the best sensitivity at different times during the course of disease. The clinical specificity was greater than 95% for all tests except for the Euroimmun IgA assay. The overall agreement with the presence of neutralizing antibodies ranged from 62.2% (95%CI; 56.0-68.1) for bioMérieux IgM to 91.2% (87.0-94.2) for Siemens. The lowest negative percent agreement (NPA) was found with the Wantai Total Ab assay (NPA 33% (21.1-48.3)). The NPA for other total Ab or IgG assays targeting the S or the RBD was 80.7% (66.7-89.7), 90.3% (78.1-96.1), and 96.8% (86.8-99.3) for Siemens, bioMérieux IgG, and DiaSorin, respectively. None of the commercial assays have sufficient performance to detect a neutralizing titer of 80 (AUC < 0.76).

CONCLUSIONS

Although some assays show a better agreement with VNT than others, the present findings emphasize that commercialized serological tests, including those targeting the RBD, cannot substitute a VNT for the assessment of functional antibody response.

Prevalence of Immunoglobulin G (IgG) Against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and Evaluation of a Rapid MEDsan IgG Test in Children Seeking Medical Care

In a sample of 208 children seeking medical care, seropositivity rate of anti-SARS-CoV-2 IgG antibodies was 8.7%, suggesting a similar infection rate to that observed in adults, but >100-fold the incidence of RT-PCR-confirmed pediatric cases. Compared to the gold-standard combined ELISA+immunofluorescence, the MEDsan IgG rapid diagnostic test performed accurately.

Head-to-Head Evaluation of Five Automated SARS-CoV-2 Serology Immunoassays in Various Prevalence Settings

Purpose: To assess the diagnostic performances of five automated anti-SARS-CoV-2 immunoassays, Epitope (N), Diasorin (S1/S2), Euroimmun (S1), Roche N (N), and Roche S (S-RBD), and to provide a testing strategy based on pre-test probability. Methods: We assessed the receiver operating characteristic (ROC) areas under the curve (AUC) values, along with the sensitivity, specificity, positive predictive values (PPVs), and negative predictive values (NPVs), of each assay using a validation sample set of 172 COVID-19 sera and 185 negative controls against a validated S1-immunofluorescence as a reference method. The three assays displaying the highest AUCs were selected for further serodetection of 2033 sera of a large population-based cohort. Results: In the validation analysis (pre-test probability: 48.1%), Roche N, Roche S and Euroimmun showed the highest discriminant accuracy (AUCs: 0.99, 0.98, and 0.98) with PPVs and NPVs above 96% and 94%, respectively. In the population-based cohort (pre-test probability: 6.2%) these three assays displayed AUCs above 0.97 and PPVs and NPVs above 90.5% and 99.4%, respectively. A sequential strategy using an anti-S assay as screening test and an anti-N as confirmatory assays resulted in a 96.7% PPV and 99.5% NPV, respectively. Conclusions: Euroimmun and both Roche assays performed equally well in high pre-test probability settings. At a lower prevalence, sequentially combining anti-S and anti-N assays resulted in the optimal trade-off between diagnostic performances and operational considerations.

Evaluation of 11 SARS-CoV-2 antibody tests by using samples from patients with defined IgG antibody titers

We evaluated the performance of 11 SARS-CoV-2 antibody tests using a reference set of heat-inactivated samples from 278 unexposed persons and 258 COVID-19 patients, some of whom contributed serial samples. The reference set included samples with a variation in SARS-CoV-2 IgG antibody titers, as determined by an in-house immunofluorescence assay (IFA). The five evaluated rapid diagnostic tests had a specificity of 99.0% and a sensitivity that ranged from 56.3 to 81.6% and decreased with low IFA IgG titers. The specificity was > 99% for five out of six platform-based tests, and when assessed using samples collected ≥ 22 days after symptom onset, two assays had a sensitivity of > 96%. These two assays also detected samples with low IFA titers more frequently than the other assays. In conclusion, the evaluated antibody tests showed a heterogeneity in their performances and only a few tests performed well with samples having low IFA IgG titers, an important aspect for diagnostics and epidemiological investigations.

Error rates in SARS-CoV-2 testing examined with Bayes' theorem

The SARS-CoV-2 pandemic has created a demand for large scale testing, as part of the effort to understand and control transmission. It is important to quantify the error rates of test equipment under field conditions, which might differ significantly from those obtained in the laboratory. A literature review on SARS-CoV-2 reverse-transcription polymerase chain reaction (RT-PCR) is used to construct a clinical test confusion matrix. A simple correction method for bulk test results is then demonstrated with examples. The required sensitivity and specificity of a test are explored for societal needs and use cases, before a sequential analysis of common example scenarios is explored. The analysis suggests that many of the people with mild symptoms and positive test results are unlikely to be infected with SARS-CoV-2 in some regions. It is concluded that current and foreseen alternative tests can not be used to "clear" people as being non-infected. Recommendations are given that regional authorities must establish a programme to monitor operational test characteristics before launching large scale testing; and that large scale testing for tracing infection networks in some regions is not viable, but may be possible in a focused way that does not exceed the working capacity of the laboratories staffed by competent experts. RT-PCR tests can not be solely relied upon as the gold standard for SARS-CoV-2 diagnosis at scale, instead clinical assessment supported by a range of expert diagnostic tests should be used.

Performance of 30 commercial SARS-CoV-2 serology assays in testing symptomatic COVID-19 patients

We report evaluation of 30 assays' (17 rapid tests (RDTs) and 13 automated/manual ELISA/CLIA assay (IAs)) clinical performances with 2594 sera collected from symptomatic patients with positive SARS-CoV-2 rRT-PCR on a respiratory sample, and 1996 pre-epidemic serum samples expected to be negative. Only 4 RDT and 3 IAs fitted both specificity (> 98%) and sensitivity (> 90%) criteria according to French recommendations. Serology may offer valuable information during COVID-19 pandemic, but inconsistent performances observed among the 30 commercial assays evaluated, which underlines the importance of independent evaluation before clinical implementation.

COVID-19 Antibody Tests and Their Limitations

COVID-19, caused by the SARS-CoV-2 virus, has developed into a global health crisis, causing over 2 million deaths and changing people's daily life the world over. Current main-stream diagnostic methods in the laboratory include nucleic acid PCR tests and direct viral antigen tests for detecting active infections, and indirect human antibody tests specific to SARS-CoV-2 to detect prior exposure. In this Perspective, we briefly describe the PCR and antigen tests and then focus mainly on existing antibody tests and their limitations including inaccuracies and possible causes of unreliability. False negatives in antibody immunoassays can arise from assay formats, selection of viral antigens and antibody types, diagnostic testing windows, individual variance, and fluctuation in antibody levels. Reasons for false positives in antibody immunoassays mainly involve antibody cross-reactivity from other viruses, as well as autoimmune disease. The spectrum bias has an effect on both the false negatives and false positives. For assay developers, not only improvement of assay formats but also selection of viral antigens and isotopes of human antibodies need to be carefully considered to improve sensitivity and specificity. For clinicians, the factors influencing the accuracy of assays must be kept in mind to test patients using currently imperfect but available tests with smart tactics and realistic interpretation of the test results.

Evaluation of 18 commercial serological assays for the detection of antibodies against SARS-CoV-2 in paired serum samples

A variety of serological tests have been developed to detect the presence of antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We evaluated the performance of 18 commercially available SARS-CoV-2 antibody assays. Early (6-8 days after the start of symptoms) and late sera (>14 days) from ICU patients (n=10 and n=16, respectively) and healthcare workers (n=5 and n=9, respectively) were included. Additionally, 22 sera were included to detect potential cross-reactivity. Test characteristics were determined for the 18 assays. In >14 days samples, the Vircell IgG and Wantai Ig ELISAs had superior sensitivity compared to the other ELISAs (96%). Furthermore, the Roche Ig, the Epitope Diagnostics IgM, Wantai IgM, Euroimmun IgG, and IgA all showed a specificity of 100%. The POCTs of Boson Biotech and ACRO Biotech showed the highest sensitivities: 100% and 96% (83.5-99.8), respectively. The POCT of Orient Gene Biotech, VOMED Diagnostics, and Coris-Bioconcept showed highest specificities (100%). For the IgM and IgA assays, the Euroimmun IgA test showed the highest sensitivity in early samples: 46.7% (23.5-70.9) to 53.3% (29.1-76.5). In general, all tests performed better in patients with severe symptoms (ICU patients). We conclude that the Wantai Ig and Vircell IgG ELISAs may be suitable for diagnostic purposes. The IgM/IgA tests performed poorer than their IgG/Ig counterparts but may have a role in diagnoses of SARS-CoV-2 in a population in which the background seroprevalence of IgG high, and IgM and/or IgA may distinguish between acute or past infection.

Accuracy of serological testing for SARS-CoV-2 antibodies: First results of a large mixed-method evaluation study

BACKGROUND

Serological immunoassays that can identify protective immunity against SARS-CoV-2 are needed to adapt quarantine measures, assess vaccination responses, and evaluate donor plasma. To date, however, the utility of such immunoassays remains unclear. In a mixed-design evaluation study, we compared the diagnostic accuracy of serological immunoassays that are based on various SARS-CoV-2 proteins and assessed the neutralizing activity of antibodies in patient sera.

METHODS

Consecutive patients admitted with confirmed SARS-CoV-2 infection were prospectively followed alongside medical staff and biobank samples from winter 2018/2019. An in-house enzyme-linked immunosorbent assay utilizing recombinant receptor-binding domain (RBD) of the SARS-CoV-2 spike protein was developed and compared to three commercially available enzyme-linked immunosorbent assays (ELISAs) targeting the nucleoprotein (N), the S1 domain of the spike protein (S1), and a lateral flow immunoassay (LFI) based on full-length spike protein. Neutralization assays with live SARS-CoV-2 were performed.

RESULTS

One thousand four hundred and seventy-seven individuals were included comprising 112 SARS-CoV-2 positives (defined as a positive real-time PCR result; prevalence 7.6%). IgG seroconversion occurred between day 0 and day 21. While the ELISAs showed sensitivities of 88.4% for RBD, 89.3% for S1, and 72.9% for N protein, the specificity was above 94% for all tests. Out of 54 SARS-CoV-2 positive individuals, 96.3% showed full neutralization of live SARS-CoV-2 at serum dilutions ≥ 1:16, while none of the 6 SARS-CoV-2-negative sera revealed neutralizing activity.

CONCLUSIONS

ELISAs targeting RBD and S1 protein of SARS-CoV-2 are promising immunoassays which shall be further evaluated in studies verifying diagnostic accuracy and protective immunity against SARS-CoV-2.

Viral infection neutralization tests: A focus on severe acute respiratory syndrome-coronavirus-2 with implications for convalescent plasma therapy

Viral neutralization tests (VNTs) have long been considered old-fashioned tricks in the armamentarium of fundamental virology, with laboratory implementation for a limited array of viruses only. Nevertheless, they represent the most reliable surrogate of potency for passive immunotherapies, such as monoclonal or polyclonal antibody therapy. The recent interest around therapy with convalescent plasma or monoclonal antibodies for the Covid-19 pandemic has paralleled the revival of VNTs. We review here the available methods by dissecting variations for each fundamental component of the VNT (i.e., virus type and dose, replication-competent cell line, serum, and detection system).

Evidence of early circulation of SARS-CoV-2 in France: findings from the population-based "CONSTANCES" cohort

Using serum samples routinely collected in 9144 adults from a French general population-based cohort, we identified 353 participants with a positive anti-SARS-CoV-2 IgG test, among whom 13 were sampled between November 2019 and January 2020 and were confirmed by neutralizing antibodies testing. Investigations in 11 of these participants revealed experience of symptoms possibly related to a SARS-CoV-2 infection or situations at risk of potential SARS-CoV-2 exposure. This suggests early circulation of SARS-CoV-2 in Europe.

Evaluation of Antibody Response in Symptomatic and Asymptomatic COVID-19 Patients and Diagnostic Assessment of New IgM/IgG ELISA Kits

This study aims to study the immune response and evaluate the performances of four new IgM and five IgG enzyme-linked immunosorbent assay (ELISA) kits for detecting anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies against different antigens in symptomatic and asymptomatic coronavirus disease 2019 (COVID-19) patients. A total of 291 samples collected from symptomatic and asymptomatic RT-PCR-confirmed patients were used to evaluate the ELISA kits' performance (EDI, AnshLabs, DiaPro, NovaLisa, and Lionex). The sensitivity was measured at three different time-intervals post symptoms onset or positive SARS-CoV-2 RT-PCR test (≤14, 14-30, >30 days). The specificity was investigated using 119 pre-pandemic serum samples. The sensitivity of all IgM kits gradually decreased with time, ranging from 48.7% (EDI)-66.4% (Lionex) at ≤14 days, 29.1% (NovaLisa)-61.8% (Lionex) at 14-30 days, and 6.0% (AnshLabs)-47.9% (Lionex) at >30 days. The sensitivity of IgG kits increased with time, peaking in the latest interval (>30 days) at 96.6% (Lionex). Specificity of IgM ranged from 88.2% (Lionex)-99.2% (EDI), while IgG ranged from 75.6% (DiaPro)-98.3% (Lionex). Among all RT-PCR-positive patients, 23 samples (7.9%) were seronegative by all IgG kits, of which only seven samples (30.4%) had detectable IgM antibodies. IgM assays have variable and low sensitivity, thus considered a poor marker for COVID-19 diagnosis. IgG assays can miss at least 8% of RT-PCR-positive cases.

Systemic and mucosal antibody responses specific to SARS-CoV-2 during mild versus severe COVID-19

BACKGROUND

Whereas severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibody tests are increasingly being used to estimate the prevalence of SARS-CoV-2 infection, the determinants of these antibody responses remain unclear.

OBJECTIVES

Our aim was to evaluate systemic and mucosal antibody responses toward SARS-CoV-2 in mild versus severe coronavirus disease 2019 (COVID-19) cases.

METHODS

Using immunoassays specific for SARS-CoV-2 spike proteins, we determined SARS-CoV-2-specific IgA and IgG in sera and mucosal fluids of 2 cohorts, including SARS-CoV-2 PCR-positive patients (n = 64) and PCR-positive and PCR-negtive health care workers (n = 109).

RESULTS

SARS-CoV-2-specific serum IgA titers in patients with mild COVID-19 were often transiently positive, whereas serum IgG titers remained negative or became positive 12 to 14 days after symptom onset. Conversely, patients with severe COVID-19 showed a highly significant increase of SARS-CoV-2-specific serum IgA and IgG titers after symptom onset. Very high titers of SARS-CoV-2-specific serum IgA were correlated with severe acute respiratory distress syndrome. Interestingly, some health care workers with negative SARS-CoV-2-specific serum antibody titers showed SARS-CoV-2-specific IgA in mucosal fluids with virus-neutralizing capacity in some cases. SARS-CoV-2-specific IgA titers in nasal fluids were inversely correlated with age.

CONCLUSIONS

Systemic antibody production against SARS-CoV-2 develops mainly in patients with severe COVID-19, with very high IgA titers seen in patients with severe acute respiratory distress syndrome, whereas mild disease may be associated with transient production of SARS-CoV-2-specific antibodies but may stimulate mucosal SARS-CoV-2-specific IgA secretion.

A highly specific and sensitive serological assay detects SARS-CoV-2 antibody levels in COVID-19 patients that correlate with neutralization

OBJECTIVE

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic challenges national health systems and the global economy. Monitoring of infection rates and seroprevalence can guide public health measures to combat the pandemic. This depends on reliable tests on active and former infections. Here, we set out to develop and validate a specific and sensitive enzyme linked immunosorbent assay (ELISA) for detection of anti-SARS-CoV-2 antibody levels.

METHODS

In our ELISA, we used SARS-CoV-2 receptor-binding domain (RBD) and a stabilized version of the spike (S) ectodomain as antigens. We assessed sera from patients infected with seasonal coronaviruses, SARS-CoV-2 and controls. We determined and monitored IgM-, IgA- and IgG-antibody responses towards these antigens. In addition, for a panel of 22 sera, virus neutralization and ELISA parameters were measured and correlated.

RESULTS

The RBD-based ELISA detected SARS-CoV-2-directed antibodies, did not cross-react with seasonal coronavirus antibodies and correlated with virus neutralization (R2 = 0.89). Seroconversion started at 5 days after symptom onset and led to robust antibody levels at 10 days after symptom onset. We demonstrate high specificity (99.3%; N = 1000) and sensitivity (92% for IgA, 96% for IgG and 98% for IgM; > 10 days after PCR-proven infection; N = 53) in serum.

CONCLUSIONS

With the described RBD-based ELISA protocol, we provide a reliable test for seroepidemiological surveys. Due to high specificity and strong correlation with virus neutralization, the RBD ELISA holds great potential to become a preferred tool to assess thresholds of protective immunity after infection and vaccination.

Systemic and mucosal antibody responses specific to SARS-CoV-2 during mild versus severe COVID-19

BACKGROUND

Whereas severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibody tests are increasingly being used to estimate the prevalence of SARS-CoV-2 infection, the determinants of these antibody responses remain unclear.

OBJECTIVES

Our aim was to evaluate systemic and mucosal antibody responses toward SARS-CoV-2 in mild versus severe coronavirus disease 2019 (COVID-19) cases.

METHODS

Using immunoassays specific for SARS-CoV-2 spike proteins, we determined SARS-CoV-2-specific IgA and IgG in sera and mucosal fluids of 2 cohorts, including SARS-CoV-2 PCR-positive patients (n = 64) and PCR-positive and PCR-negtive health care workers (n = 109).

RESULTS

SARS-CoV-2-specific serum IgA titers in patients with mild COVID-19 were often transiently positive, whereas serum IgG titers remained negative or became positive 12 to 14 days after symptom onset. Conversely, patients with severe COVID-19 showed a highly significant increase of SARS-CoV-2-specific serum IgA and IgG titers after symptom onset. Very high titers of SARS-CoV-2-specific serum IgA were correlated with severe acute respiratory distress syndrome. Interestingly, some health care workers with negative SARS-CoV-2-specific serum antibody titers showed SARS-CoV-2-specific IgA in mucosal fluids with virus-neutralizing capacity in some cases. SARS-CoV-2-specific IgA titers in nasal fluids were inversely correlated with age.

CONCLUSIONS

Systemic antibody production against SARS-CoV-2 develops mainly in patients with severe COVID-19, with very high IgA titers seen in patients with severe acute respiratory distress syndrome, whereas mild disease may be associated with transient production of SARS-CoV-2-specific antibodies but may stimulate mucosal SARS-CoV-2-specific IgA secretion.

Estimating the cumulative incidence of SARS-CoV-2 with imperfect serological tests: Exploiting cutoff-free approaches

Large-scale serological testing in the population is essential to determine the true extent of the current SARS-CoV-2 pandemic. Serological tests measure antibody responses against pathogens and use predefined cutoff levels that dichotomize the quantitative test measures into sero-positives and negatives and use this as a proxy for past infection. With the imperfect assays that are currently available to test for past SARS-CoV-2 infection, the fraction of seropositive individuals in serosurveys is a biased estimator of the cumulative incidence and is usually corrected to account for the sensitivity and specificity. Here we use an inference method-referred to as mixture-model approach-for the estimation of the cumulative incidence that does not require to define cutoffs by integrating the quantitative test measures directly into the statistical inference procedure. We confirm that the mixture model outperforms the methods based on cutoffs, leading to less bias and error in estimates of the cumulative incidence. We illustrate how the mixture model can be used to optimize the design of serosurveys with imperfect serological tests. We also provide guidance on the number of control and case sera that are required to quantify the test's ambiguity sufficiently to enable the reliable estimation of the cumulative incidence. Lastly, we show how this approach can be used to estimate the cumulative incidence of classes of infections with an unknown distribution of quantitative test measures. This is a very promising application of the mixture-model approach that could identify the elusive fraction of asymptomatic SARS-CoV-2 infections. An R-package implementing the inference methods used in this paper is provided. Our study advocates using serological tests without cutoffs, especially if they are used to determine parameters characterizing populations rather than individuals. This approach circumvents some of the shortcomings of cutoff-based methods at exactly the low cumulative incidence levels and test accuracies that we are currently facing in SARS-CoV-2 serosurveys.

Disease Severity, Fever, Age, and Sex Correlate With SARS-CoV-2 Neutralizing Antibody Responses

Clinical trials on the use of COVID-19 convalescent plasma remain inconclusive. While data on safety is increasingly available, evidence for efficacy is still sparse. Subgroup analyses hint to a dose-response relationship between convalescent plasma neutralizing antibody levels and mortality. In particular, patients with primary and secondary antibody deficiency might benefit from this approach. However, testing of neutralizing antibodies is limited to specialized biosafety level 3 laboratories and is a time- and labor-intense procedure. In this single center study of 206 COVID-19 convalescent patients, clinical data, results of commercially available ELISA testing of SARS-CoV-2 spike-IgG and -IgA, and levels of neutralizing antibodies, determined by plaque reduction neutralization testing (PRNT), were analyzed. At a medium time point of 58 days after symptom onset, only 12.6% of potential plasma donors showed high levels of neutralizing antibodies (PRNT50 ≥ 1:320). Multivariable proportional odds logistic regression analysis revealed need for hospitalization due to COVID-19 (odds ratio 6.87; p-value 0.0004) and fever (odds ratio 3.00; p-value 0.0001) as leading factors affecting levels of SARS-CoV-2 neutralizing antibody titers in convalescent plasma donors. Using penalized estimation, a predictive proportional odds logistic regression model including the most important variables hospitalization, fever, age, sex, and anosmia or dysgeusia was developed. The predictive discrimination for PRNT50 ≥ 1:320 was reasonably good with AUC: 0.86 (with 95% CI: 0.79-0.92). Combining clinical and ELISA-based pre-screening, assessment of neutralizing antibodies could be spared in 75% of potential donors with a maximal loss of 10% of true positives (PRNT50 ≥ 1:320).

Humoral and Cellular Response of Frontline Health Care Workers Infected by SARS-CoV-2 in Nice, France: A Prospective Single-Center Cohort Study

Frontline health care workers (HCWs) have been particularly exposed to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) since the start of the pandemic but the clinical features and immune responses of those infected with SARS-CoV-2 have not been well described. In a prospective single center cohort study, we enrolled 196 frontline HCWs exposed to the SARS-Cov-2 and 60 patients with moderate and severe forms of the coronavirus disease 2019 (COVID-19). Serological tests and cytokines assay were performed to analyze SARS-CoV-2-specific humoral and cellular immunity. Of the 196 HCWs tested, 15% had specific antibodies against SARS-CoV-2 and 45% of seropositive HCWs were strictly asymptomatic. However, in comparison to moderate and severe forms, HCWs with mild or asymptomatic forms of COVID-19 showed lower specific IgA and IgG peaks, consistent with their mild symptoms, and a robust immune cellular response, illustrated by a high production of type I and II interferons. Further studies are needed to evaluate whether this interferon functional immune assay, routinely applicable, can be useful in predicting the risk of severe forms of COVID-19.

Diagnostic Efficiency of Three Fully Automated Serology Assays and Their Correlation with a Novel Surrogate Virus Neutralization Test in Symptomatic and Asymptomatic SARS-COV-2 Individuals

To support the deployment of serology assays for population screening during the COVID-19 pandemic, we compared the performance of three fully automated SARS-CoV-2 IgG assays: Mindray CL-900i® (target: spike [S] and nucleocapsid [N]), BioMérieux VIDAS®3 (target: receptor-binding domain [RBD]) and Diasorin LIAISON®XL (target: S1 and S2 subunits). A total of 111 SARS-CoV-2 RT-PCR- positive samples collected at ≥ 21 days post symptom onset, and 127 pre-pandemic control samples were included. Diagnostic performance was assessed in correlation to RT-PCR and a surrogate virus-neutralizing test (sVNT). Moreover, cross-reactivity with other viral antibodies was investigated. Compared to RT-PCR, LIAISON®XL showed the highest overall specificity (100%), followed by VIDAS®3 (98.4%) and CL-900i® (95.3%). The highest sensitivity was demonstrated by CL-900i® (90.1%), followed by VIDAS®3 (88.3%) and LIAISON®XL (85.6%). The sensitivity of all assays was higher in symptomatic patients (91.1-98.2%) compared to asymptomatic patients (78.4-80.4%). In correlation to sVNT, all assays showed excellent sensitivities (92.2-96.1%). In addition, VIDAS®3 demonstrated the best correlation (r = 0.75) with the sVNT. The present study provides insights on the performance of three fully automated assays, which could help diagnostic laboratories in the choice of a particular assay according to the intended use.

Comparison of Five Serological Assays for the Detection of SARS-CoV-2 Antibodies

Serological assays can contribute to the estimation of population proportions with previous immunologically relevant contact with the Severe Acute Respiratory Syndrome Corona Virus 2 (SARS-CoV-2) virus. In this study, we compared five commercially available diagnostic assays for the diagnostic identification of SARS-CoV-2-specific antibodies. Depending on the assessed immunoglobulin subclass, recorded sensitivity ranged from 17.0% to 81.9% with best results for immunoglobulin G. Specificity with blood donor sera ranged from 90.2% to 100%, with sera from EBV patients it ranged from 84.3% to 100%. Agreement from fair to nearly perfect was recorded depending on the immunoglobulin class between the assays, the with best results being found for immunoglobulin G. Only for this immunoglobulin class was the association between later sample acquisition times (about three weeks after first positive PCR results) and positive serological results in COVID-19 patients confirmed. In conclusion, acceptable and comparable reliability for the assessed immunoglobulin G-specific assays could be shown, while there is still room for improvement regarding the reliability of the assays targeting the other immunoglobulin classes.

Characteristics of Three Different Chemiluminescence Assays for Testing for SARS-CoV-2 Antibodies

Several tests based on chemiluminescence immunoassay techniques have become available to test for SARS-CoV-2 antibodies. There is currently insufficient data on serology assay performance beyond 35 days after symptoms onset. We aimed to evaluate SARS-CoV-2 antibody tests on three widely used platforms. A chemiluminescent microparticle immunoassay (CMIA; Abbott Diagnostics, USA), a luminescence immunoassay (LIA; Diasorin, Italy), and an electrochemiluminescence immunoassay (ECLIA; Roche Diagnostics, Switzerland) were investigated. In a multigroup study, sensitivity was assessed in a group of participants with confirmed SARS-CoV-2 (n = 145), whereas specificity was determined in two groups of participants without evidence of COVID-19 (i.e., healthy blood donors, n = 191, and healthcare workers, n = 1002). Receiver operating characteristic (ROC) curves, multilevel likelihood ratios (LR), and positive (PPV) and negative (NPV) predictive values were characterized. Finally, analytical specificity was characterized in samples with evidence of the Epstein–Barr virus (EBV) (n = 9), cytomegalovirus (CMV) (n = 7), and endemic common-cold coronavirus infections (n = 12) taken prior to the current SARS-CoV-2 pandemic. The diagnostic accuracy was comparable in all three assays (AUC 0.98). Using the manufacturers' cut-offs, the sensitivities were 90%, 95% confidence interval [84,94] (LIA), 93% [88,96] (CMIA), and 96% [91,98] (ECLIA). The specificities were 99.5% [98.9,99.8] (CMIA), 99.7% [99.3,99.9] (LIA), and 99.9% [99.5,99.98] (ECLIA). The LR at half of the manufacturers' cut-offs were 60 (CMIA), 82 (LIA), and 575 (ECLIA) for positive and 0.043 (CMIA) and 0.035 (LIA, ECLIA) for negative results. ECLIA had higher PPV at low pretest probabilities than CMIA and LIA. No interference with EBV or CMV infection was observed, whereas endemic coronavirus in some cases provided signals in LIA and/or CMIA. Although the diagnostic accuracy of the three investigated assays is comparable, their performance in low-prevalence settings is different. Introducing gray zones at half of the manufacturers' cut-offs is suggested, especially for orthogonal testing approaches that use a second assay for confirmation.

Development and characterization of an indirect ELISA to detect SARS-CoV-2 spike protein-specific antibodies

The current Severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) pandemic is a public health emergency of international concern. Sensitive and precise diagnostic tools are urgently needed. In this study, we developed a SARS-CoV-2 spike (S1) protein enzyme-linked immunosorbent assay (ELISA) to detect SARS-CoV-2-specific antibodies. The SARS-CoV-2 S1 ELISA was found to be specific [97.8% (95% CI, 96.7% - 98.5%)], reproducible and precise (intra-assay coefficient of variability (CV) 5.3%, inter-assay CV 7.9%). A standard curve and the interpolation of arbitrary ELISA units per milliliter served to reduce the variability between different tests and operators. Cross-reactivity to other human coronaviruses was addressed by using sera positive for MERS-CoV- and hCoV HKU1-specific antibodies. Monitoring antibody development in various samples of twenty-three and single samples of twenty-nine coronavirus disease 2019 (COVID−19) patients revealed seroconversion and neutralizing antibodies against authentic SARS-CoV-2 in all cases. The comparison of the SARS-CoV-2 (S1) ELISA with a commercially available assay showed a better sensitivity for the in-house ELISA.

The results demonstrate a high reproducibility, specificity and sensitivity of the newly developed ELISA, which is suitable for the detection of SARS-CoV-2 S1 protein-specific antibody responses.

•

A highly sensitive and specific SARS-CoV-2 S1 ELISA was developed.

•

A standard curve is included to reduce variability between assays and operators.

•

Excellent intra-assay coefficient of variability (CV) 5.3%, inter-assay CV 7.9%.

•

Good correlation to the virus neutralization test VNT₁₀₀.

Performance evaluation of five ELISA kits for detecting anti-SARS-COV-2 IgG antibodies

OBJECTIVES

To evaluate and compare the performances of five commercial ELISA assays (EDI, AnshLabs, Dia.Pro, NovaTec, and Lionex) for detecting anti-SARS-CoV-2 IgG.

METHODS

Seventy negative control samples (collected before the COVID-19 pandemic) and samples from 101 RT-PCR-confirmed SARS-CoV-2 patients (collected at different time points from symptom onset: ≤7, 8-14 and >14 days) were used to compare the sensitivity, specificity, agreement, and positive and negative predictive values of each assay with RT-PCR. A concordance assessment between the five assays was also conducted. Cross-reactivity with other HCoV, non-HCoV respiratory viruses, non-respiratory viruses, and nuclear antigens was investigated.

RESULTS

Lionex showed the highest specificity (98.6%; 95% CI 92.3-99.8), followed by EDI and Dia.Pro (97.1%; 95% CI 90.2-99.2), NovaTec (85.7%; 95% CI 75.7-92.1), then AnshLabs (75.7%; 95% CI 64.5-84.2). All ELISA kits cross-reacted with one anti-MERS IgG-positive sample, except Lionex. The sensitivity was low during the early stages of the disease but improved over time. After 14 days from symptom onset, Lionex and NovaTec showed the highest sensitivity at 87.9% (95% CI 72.7-95.2) and 86.4% (95% CI 78.5-91.7), respectively. The agreement with RT-PCR results based on Cohen's kappa was as follows: Lionex (0.89) > NovaTec (0.70) > Dia.Pro (0.69) > AnshLabs (0.63) > EDI (0.55).

CONCLUSION

The Lionex and NovaLisa IgG ELISA kits, demonstrated the best overall performance.

How Useful is COVID-19 Antibody Testing - A Current Assessment for Oncologists

The coronavirus disease 2019 (COVID-19) pandemic due to infection by a new human coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has seriously disrupted the provision of oncology services and their uptake. Antibody testing, both at an individual level and of populations, has been widely viewed to be a key activity for guiding the options for treatment of high-risk individuals, as well as the implementation of safe control of infection measures. Ideally, the detection of a specific antibody should signify that all individuals tested have been infected by SARS-CoV-2 and that in the case of specific IgG that they are immune to further infection. This would enable SARS-CoV-2-infected individuals to be appropriately managed and healthcare workers shown to be immune to return to work where they would no longer pose a risk to their patients or be at risk themselves. Unfortunately, this is not the case for COVID-19, where it has been shown that immunity may not be protective, and seroconversion delayed or absent. The variability in antibody test performance, particularly that of lateral flow assays, has caused confusion for the public and healthcare professions alike. Many antibody test devices have been made available without independent evaluations and these may lack both adequate sensitivity and specificity. This review seeks to educate healthcare workers, particularly those working in oncology, of the current benefits and limitations of SARS-CoV-2 antibody testing.

Comparison of Four SARS-CoV-2 Neutralization Assays

Neutralizing antibodies are a major correlate of protection for many viruses including the novel coronavirus SARS-CoV-2. Thus, vaccine candidates should potently induce neutralizing antibodies to render effective protection from infection. A variety of in vitro assays for the detection of SARS-CoV-2 neutralizing antibodies has been described. However, validation of the different assays against each other is important to allow comparison of different studies. Here, we compared four different SARS-CoV-2 neutralization assays using the same set of patient samples. Two assays used replication competent SARS-CoV-2, a focus forming assay and a TCID50-based assay, while the other two assays used replication defective lentiviral or vesicular stomatitis virus (VSV)-based particles pseudotyped with SARS-CoV-2 spike. All assays were robust and produced highly reproducible neutralization titers. Titers of neutralizing antibodies correlated well between the different assays and with the titers of SARS-CoV-2 S-protein binding antibodies detected in an ELISA. Our study showed that commonly used SARS-CoV-2 neutralization assays are robust and that results obtained with different assays are comparable.

Quick COVID-19 Healers Sustain Anti-SARS-CoV-2 Antibody Production

Antibodies are key immune effectors that confer protection against pathogenic threats. The nature and longevity of the antibody response to SARS-CoV-2 infection are not well defined. We charted longitudinal antibody responses to SARS-CoV-2 in 92 subjects after symptomatic COVID-19. Antibody responses to SARS-CoV-2 are unimodally distributed over a broad range, with symptom severity correlating directly with virus-specific antibody magnitude. Seventy-six subjects followed longitudinally to ∼100 days demonstrated marked heterogeneity in antibody duration dynamics. Virus-specific IgG decayed substantially in most individuals, whereas a distinct subset had stable or increasing antibody levels in the same time frame despite similar initial antibody magnitudes. These individuals with increasing responses recovered rapidly from symptomatic COVID-19 disease, harbored increased somatic mutations in virus-specific memory B cell antibody genes, and had persistent higher frequencies of previously activated CD4+ T cells. These findings illuminate an efficient immune phenotype that connects symptom clearance speed to differential antibody durability dynamics.

Systematic analysis, identification, and use of CRISPR/Cas13a-associated crRNAs for sensitive and specific detection of the lcrV gene of Yersinia pestis

CRISPR-associated proteins that produce a signal in the presence of a target nucleic acid represent potentially powerful tools for diagnostics, but they also exhibit shortfalls that plague many CRISPR systems. For instance, not all targets elicit robust activity, which challenges the timely development of sensitive assays, and though many such tests have been reported, they often avoid discussion of the crRNA design and screening process. Here, motivated by the desire to detect the Yersinia pestis lcrV virulence gene, we detail the process involved in developing components for a CRISPR-based test that provides sensitive and specific identification of this sequence using Cas13a. This includes detailing the diversity of crRNA performance, identifying sequence that enable detection with attomolar sensitivity and species-level specificity, and presenting a method for simple streamlining of the crRNA screening process to allow for the high-throughput testing required for developing assay design rules in the future.

Immunological Assessment of Pediatric Multisystem Inflammatory Syndrome Related to Coronavirus Disease 2019

BACKGROUND

Recently, cases of multisystem inflammatory syndrome in children (MIS-C) associated with coronavirus disease 2019 (COVID-19) have been reported worldwide. Negative polymerase chain reaction (RT-PCR) testing associated with positive serology in most of the cases suggests a postinfectious syndrome. Because the pathophysiology of this syndrome is still poorly understood, extensive virological and immunological investigations are needed.

METHODS

We report a series of 4 pediatric patients admitted to Geneva University Hospitals with persistent fever and laboratory evidence of inflammation meeting the published definition of MIS-C related to COVID-19, to whom an extensive virological and immunological workup was performed.

RESULTS

RT-PCRs on multiple anatomical compartments were negative, whereas anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin A (IgA) and immunoglobulin G (IgG) were strongly positive by enzyme-linked immunosorbent assay and immunofluorescence. Both pseudoneutralization and full virus neutralization assays showed the presence of neutralizing antibodies in all children, confirming a recent infection with SARS-CoV-2. The analyses of cytokine profiles revealed an elevation in all cytokines, as reported in adults with severe COVID-19. Although differing in clinical presentation, some features of MIS-C show phenotypic overlap with hemophagocytic lymphohistiocytosis (HLH). In contrast to patients with primary HLH, our patients showed normal perforin expression and natural killer (NK) cell degranulation. The levels of soluble interleukin (IL)-2 receptor (sIL-2R) correlated with the severity of disease, reflecting recent T-cell activation.

CONCLUSION

Our findings suggest that MIS-C related to COVID-19 is caused by a postinfectious inflammatory syndrome associated with an elevation in all cytokines, and markers of recent T-cell activation (sIL-2R) occurring despite a strong and specific humoral response to SARS-CoV-2. Further functional and genetic analyses are essential to better understand the mechanisms of host-pathogen interactions.

Daily Viral Kinetics and Innate and Adaptive Immune Response Assessment in COVID-19: a Case Series

Viral shedding patterns and their correlations with immune responses are still poorly characterized in mild coronavirus (CoV) disease 2019 (COVID-19). We monitored shedding of viral RNA and infectious virus and characterized the immune response kinetics of the first five patients quarantined in Geneva, Switzerland. High viral loads and infectious virus shedding were observed from the respiratory tract despite mild symptoms, with isolation of infectious virus and prolonged positivity by reverse transcriptase PCR (RT-PCR) until days 7 and 19 after symptom onset, respectively. Robust innate responses characterized by increases in activated CD14+ CD16+ monocytes and cytokine responses were observed as early as 2 days after symptom onset. Cellular and humoral severe acute respiratory syndrome (SARS)-CoV-2-specific adaptive responses were detectable in all patients. Infectious virus shedding was limited to the first week after symptom onset. A strong innate response, characterized by mobilization of activated monocytes during the first days of infection and SARS-CoV-2-specific antibodies, was detectable even in patients with mild disease.IMPORTANCE This work is particularly important because it simultaneously assessed the virology, immunology, and clinical presentation of the same subjects, whereas other studies assess these separately. We describe the detailed viral and immune profiles of the first five patients infected by SARS-CoV-2 and quarantined in Geneva, Switzerland. Viral loads peaked at the very beginning of the disease, and infectious virus was shed only during the early acute phase of disease. No infectious virus could be isolated by culture 7 days after onset of symptoms, while viral RNA was still detectable for a prolonged period. Importantly, we saw that all patients, even those with mild symptoms, mount an innate response sufficient for viral control (characterized by early activated cytokines and monocyte responses) and develop specific immunity as well as cellular and humoral SARS-CoV-2-specific adaptive responses, which already begin to decline a few months after the resolution of symptoms.