High SARS-CoV-2 seroprevalence among street adolescents in Lomé, Togo, 2021 (preprint)

Background. There is almost no data on the circulation of SARS-CoV-2 among street adolescents. We conducted a study to document the immunization status of street adolescents in Togo against different variants of SARS-CoV-2. Methods. A cross-sectional study was carried out in 2021 in Lomé, the city with the highest number of COVID 19 cases in Togo (60%). Adolescents aged 13- and 19 years old living on the street were eligible for inclusion. A standardized questionnaire was administered face-to-face to adolescents. A sample of blood was taken and aliquots of plasma were transported to the virology laboratory of the Hôpital Bichat-Claude Bernard (Paris, France). SARS-CoV-2 anti-S and anti-N IgG were measured using chemiluminescent microparticle immunoassay. A quantitative miniaturized and parallel-arranged ELISA assay was used to detect IgG antibodies specifically directed against the different SARS-CoV-2 Variants of Concern (VOC). Results. A total of 299 street adolescents (5.2% female), median age 15 years, interquartile range [14-17], were included in this study. The prevalence of SARS-CoV-2 infection was 63.5% (95%CI: 57.8-69.0). Specific-IgG against the ancestral Wuhan strain was developed by 92.0% of subjects. The proportion of patients being immunized against each VOC was 86.8%, 51.1%, 56.3%, 60.0, and 30.5% for the Alpha, Beta, Gamma, Delta, and Omicron VOCs, respectively. Conclusion. This study showed a very high prevalence with approximately 2/3 of Togolese street adolescents having antibodies to SARS-CoV-2 due to a previous infection. These results confirm an under-reporting of COVID-19 cases in Togo, questioning the hypothesis of low virus circulation in Togo and even in Africa.

Phylodynamics of SARS-CoV-2 transmissions in France, Europe and the world during 2020 (preprint)

Background Although France was one of the most affected European countries by the COVID-19 pandemic in 2020, the dynamics of SARS-CoV-2 transmissions within France, Europe and worldwide remain only partially characterized during the first year of the pandemic. Methods Here, we analyzed GISAID deposited sequences from January to December 2020 (n = 638,706 sequences). To tackle the huge number of sequences without the bias of analyzing a single sequence subset, we produced 100 independent and randomly selected sequence datasets and related phylogenetic trees for different geographic scales (worldwide, European countries and French administrative regions) and time periods (first and second half of 2020). We applied a maximum likelihood discrete trait phylogeographic method to date transmission events and to estimate the geographic spread of SARS-CoV-2 to, from and within France, Europe and worldwide. Results The results unraveled two different patterns of inter- and intra-territory transmission events between the first and second half of 2020. Throughout the year, Europe was systematically associated with most of the intercontinental transmissions, for which France has played a pivotal role. SARS-CoV-2 transmissions with France were concentrated with North America and Europe (mainly Italy, Spain, United Kingdom, Belgium and Germany) during the first wave, and were limited to neighboring countries without strong intercontinental transmission during the second one. Regarding French administrative regions, the Paris area was the main source of transmissions during the first wave. But, for the second epidemic wave, it equally contributed to virus spread with Lyon and Marseille area, the two other most densely populated cities in France. Conclusion By enabling the inclusion of tens of thousands of viral sequences, this original phylogenetic strategy enabled us to robustly depict SARS-CoV-2 transmissions through France, Europe and worldwide in 2020.

Clinical phenotypes and outcomes associated with SARS-CoV-2 variant Omicron, sublineages BA.1, BA.1.1, BA.2 and impact of mutational patterns in critically ill French patients with COVID-19 (preprint)

Infection with SARS-CoV-2 variant Omicron is considered to be less severe than infection with variant Delta, with a rarer occurrence of severe disease requiring intensive care. However, a substantial number of patients infected with variant Omicron still experienced severe COVID-19. Little information is available on comorbid factors, clinical conditions and specific viral mutational patterns associated with the severity of variant Omicron infection. In this multicenter prospective cohort study, patients consecutively admitted for severe COVID-19 in 20 participating intensive care units in France between December 7th 2021 and May 1st 2022 were included. Among 259 patients for whom SARS-CoV-2 variant lineage was determined, we show that the clinical phenotype of patients infected with variant Omicron (n = 148) was different from that in those infected with variant Delta (n = 111). We observed no significant relationship between Delta and Omicron variant lineages/sublineages and 28-day mortality (adjusted odds ratio [95% confidence interval] = 0.68 [0.35–1.32]; p = 0.253). Among Omicron-infected patients, 43.2% were immunocompromised, most of whom had received two doses of vaccine or more (85.9%) but displayed a poor humoral response to vaccination (mean difference in serum anti-spike IgG antibody titers between vaccinated and non-vaccinated immunocompromised patients: 1078 BAU/mL [-319.4; 2475.0]; p = 0.160). The mortality rate of immunocompromised patients infected with variant Omicron was significantly higher than that of non-immunocompromised patients (46.9% vs 26.2%; p = 0.009). In patients infected with variant Omicron, there was no association between specific sublineages (BA.1/BA.1.1 (n = 109) and BA.2 (n = 21)) or any viral genome polymorphisms or mutational profile and the 28-day mortality.

Could faecal viral excretion explain gastrointestinal symptoms in COVID-19 patients: co- infection involvement? (preprint)

Objectives: Physiopathological mechanisms responsible for digestive symptoms during COVID-19 are still unclear. The aim of this study was to determine the influence of faecal viral shedding on digestive symptoms and propose differential diagnoses to better understand the gastrointestinal clinical spectrum during acute COVID-19.Methods: Patients were included if one stool sample was available for microbiological investigation. Microbiological analysis consisted of syndromic PCR screening, and parasitological investigation included microsporidia and multiplex protozoa PCR. SARS-CoV-2 infection was diagnosed by viral detection (on respiratory samples and frozen stool samples) and by serology when necessary. Collected epidemiological, clinical, radiological, biological data and clinical course were compared according to COVID-19 status, faecal SARS-CoV-2 shedding and co-infection status.Results: 50 COVID+ and 67 COVID- patients were included. Faecal viral shedding was detected in 50% of stool samples and was associated with higher viral load in the upper respiratory tract. There was no difference in the proportion of detected enteric pathogens between COVID-19 status. No impact was observed on clinical course regardless of COVID-19 status, faecal SARS-CoV-2 shedding and coinfection status.Conclusions: SARS-CoV-2 shedding and enteric pathogen involvement in gastrointestinal presentation is still unclear. However, differential diagnostic investigation revealed frequently occurring common enteric pathogens in COVID-19 patients.

SARS CoV-2 Genomic Characteristics and Clinical Impact of SARS-CoV-2 Viral Diversity in Critically Ill COVID-19 Patients: A Prospective Multicenter Cohort Study (preprint)

Background: SARS-CoV-2 variant of concern (VOC) α spread worldwide, including in France, at the beginning of 2021. This variant was suggested to be associated with a higher risk of mortality than other variants. Little information is available in the subset of patients with severe disease admitted in the intensive care unit (ICU). We aimed to characterize the genetic diversity of SARS-CoV-2 variants isolated from patients with severe COVID-19 in order to unravel the relationships between specific viral mutations/mutational patterns and clinical outcomes. Methods: : Prospective multicentre observational cohort study. Patients aged ≥18 years admitted in 11 ICUs from Great Paris area hospitals between October 1, 2020, and May 30, 2021 (before the introduction of VOC δ (B.617.2) in France) for acute respiratory failure (SpO2≤90% and need for supplemental oxygen or ventilator support) were included. SARS-CoV-2 infection, determined by RT-PCR testing. The primary clinical endpoint was day-28 mortality. Full-length SARS-CoV-2 genomes were sequenced by means of next-generation sequencing (Illumina COVIDSeq). Results: : 413 patients were included, 183 (44.3%) had been infected with pre-existing variants, 197 (47.7%) with variant α (B.1.1.7), and 33 (8.0%) with other variants. Patients infected with pre-existing variants were significantly older (64.9±11.9 vs 60.5±11.8 years; p=0.0005); they had significantly more frequent COPD (11.5% (n=21/183) vs 4.1% (n=8/197); p=0.009), and higher SOFA score (4 [3-8] vs 3 [2-4]; 0.0002). Day-28 mortality was not different between patients infected with pre-existing, α (B.1.1.7) or other variants (31.1% (n=57/183) vs 26.2% (n=51/197) vs 30.3% (n=10/33), respectively; p=0.550). There was no association between day-28 mortality with a specific variant or the presence of specific mutations in SARS CoV-2 genome, including 17 mutations selected in the spike protein and all 1017 non-synonymous mutations detected throughout the entire viral genome. Conclusions: : At ICU admission, patients infected with pre-existing variants had a different clinical presentation from those infected with variant α (B.1.1.7) and other variants later in the course of the pandemic, but mortality did not differ between these groups. There was no association between a specific variant or SARS CoV-2 genome mutational pattern and day-28 mortality.

Efficacy of SARS-CoV-2 vaccine in thoracic cancer patients: a prospective study supporting a third dose in patients with minimal serologic response after two vaccine doses (preprint)

HypothesisCoronavirus disease 2019 (COVID-19) resulted in a 30% mortality rate in thoracic cancer patients. Given that cancer patients were excluded from serum anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) vaccine registration trials, it is still unknown whether they would develop a protective anti-spike antibody response following vaccination. This prospective vaccine monitoring study primarily aimed to assess humoral responses to SARS-CoV2 vaccine in thoracic cancer patients. MethodsSARS-CoV2-spike antibodies were measured using Abbot ARCHITECT SARS-CoV-2 IgG immunoassay, prior to first injection of BNT162b2 mRNA vaccine, as well as at Week 4, and two-to-sixteen weeks after second vaccine dose. The factors associated with antibody response were analyzed. ResultsOverall, 306 patients, with a median age of 67.0 years (IQR=58-74), were vaccinated. Of these, 283 patients received two vaccine doses at 28-day intervals. After 4.7-month median follow-up, seven patients (2.3%) contracted proven symptomatic SARS-CoV-2 infection, with rapid favorable evolution. Of 269 serological results available beyond Day 14 post-second vaccine dose, 17 (6.3%) were still negative (<50 AU/mL) (arbitrary units/mL), while 34 (11%) were <300 AU/mL (12.5th percentile). In multivariate analysis, only age and chronic corticosteroid treatment were significantly associated with a lack of immunization. Thirty patients received a third vaccine dose, with only three patients showing persistent negative serology thereafter, whereas the others demonstrated clear seroconversion. ConclusionSARS-CoV2 vaccines were shown to be efficient in thoracic cancer patients, most of them being immunized after two doses. A third shot given to 1% of patients with persistent low antibody titers resulted in a 88% immunization rate.

Increased Risk of Severe COVID-19 in Hospitalized Patients With SARS-CoV-2 Variant of Concern Alpha Infection in France: A Multicentre Matched Cohort Study With Retrospective Data Collection (preprint)

Background: The impact of the variant of concern (VOC) Alpha on the severity of COVID-19 is debated and has to be analyzed in different epidemiological situations. We report our analysis in France.Methods: We conducted an exposed/unexposed cohort study with retrospective data collection, comparing patients infected by VOC Alpha to patients infected by historical lineages. Participants were matched on age (+/- 2.5 years), sex and region of hospitalization. The primary endpoint was the proportion of hospitalized participants with severe COVID-19, defined as a WHO-scale >5 or by the need of a non-rebreather mask, occurring up to day 29 after admission. We used a logistic regression model stratified on each matched pair and accounting for factors known to be associated with the severity of the disease (age, BMI and comorbidities) to compare the 2 groups. Findings: We included 650 pairs of patients hospitalized between Jan 1, 2021, and Feb 28, 2021, in 47 hospitals. Median age was 70 years and 61.3% of participants were male. The proportion of participants with comorbidities was high in both groups (85.0% vs 90%, p=0.004). Infection by VOC Alpha was associated with a higher risk of severe COVID-19 (41.7% vs 38.5% - aOR=1.33 95% CI [1.03-1.72]). The rate of mortality was 24.0% vs 19.0% (aHR 1.21 95% CI [0.93-1.58]).Interpretation: Infection by the VOC Alpha was associated with a higher risk of severe COVID-19 during the third COVID-19 epidemic wave in France.Clinical Trial Registration Details: Registered on ClinicalTrials.gov (NCT04863547). Funding Information: The study was funded by the ANRS Maladies Infectieuses Emergentes.Declaration of Interests: DC reports HIV grants from Janssen (2017-2018, 2019-2020), personal fees from Janssen (2018) and Gilead (2018, 2020) for lectures on HIV outside the submitted work. CC reports personal fees from Janssen (2018), MSD (2019), Gilead (2018-2020), Theratechnologies (2020) and ViiV Healthcare (2018-2020). HC reports personal fees from MSD (2020) and ViiV Healthcare (2020) for lectures on HIV. GMB reports support for attending meetings and personal fees from BMS, MSD, Janssen, Sanofi, Pfizer and Gilead for lectures outside the submitted work. JP reports support for attending meetings and personal fees from Gilead, Pfizer and Eumedica Gilead for lectures. DD reports personal fees from Gilead, ViiV Healthcare and Janssen for participation on an advisory Board. Other authors declare that they have no competing interest.Ethics Approval Statement: The study was approved by the SPILF Ethics Committee.

The 501Y.V2 SARS-CoV-2 variant has an intermediate viral load between the 501Y.V1 and the historical variants in nasopharyngeal samples from newly diagnosed COVID-19 patients (preprint)

The 501Y.V2 and the 501Y.V1 SARS-CoV-2 variants emerged and spread rapidly into the world. We analysed the RT-PCR cycle threshold values of 643 nasopharyngeal samples of COVID-19 patients at diagnosis and found that the 501Y.V2 variant presented an intermediate viral load between the 501Y.V1 and the historical variants.

Viral epidemiology and SARS-CoV-2 coinfections with other respiratory viruses during the first COVID-19 wave in Paris, France (preprint)

Abstract: Objectives: Our work assessed the prevalence of co-infections in patients with SARS-CoV-2. Methods: All patients hospitalized in a Parisian hospital during the first wave of COVID-19 were tested by mPCR if they presented ILI symptoms. Results: A total of 806 patients (21%) were positive for SARS-CoV-2, 755 (20%) were positive for other respiratory viruses. Among the SARS-CoV-2 positive patients, 49 (6%) had viral co-infections. They presented similar age, symptoms, except for fever (p=0.013) and headaches (p=0.048), than single SARS-CoV-2 infections. Conclusions: SARS-CoV-2 infected patients presenting viral co-infections had similar clinical characteristics and prognosis than patients solely infected with SARS-CoV-2.

High-risk exposure without personal protective equipment and infection with SARS-CoV-2 in healthcare workers: results of the CoV-CONTACT prospective cohort (preprint)

Objective: We aimed to estimate the risk of infection in Healthcare workers (HCWs) following a high-risk exposure without personal protective equipment (PPE). Methods: We conducted a prospective cohort in HCWs who had a high-risk exposure to SARS-CoV-2-infected subject without PPE. Daily symptoms were self-reported for 30 days, nasopharyngeal swabs for SARS-CoV-2 RT-PCR were performed at inclusion and at days 3, 5, 7 and 12, SARS-CoV-2 serology was assessed at inclusion and at day 30. Confirmed infection was defined by positive RT-PCR or seroconversion, and possible infection by one general and one specific symptom for two consecutive days. Results: Between February 5th and May 30th, 2020, 154 HCWs were enrolled within 14 days following one high-risk exposure to either a hospital patient (70/154; 46.1%) and/or a colleague (95/154; 62.5%). At day 30, 25.0% had a confirmed infection (37/148; 95%CI, 18.4%; 32.9%), and 43.9% (65/148; 95%CI, 35.9%; 52.3%) had a confirmed or possible infection. Factors independently associated with confirmed or possible SARS-CoV-2 infection were being a pharmacist or administrative assistant rather than being from medical staff (adjusted OR (aOR)=3.8, CI95%=1.3;11.2, p=0.01), and exposure to a SARS-CoV-2-infected patient rather than exposure to a SARS-CoV-2-infected colleague (aOR=2.6, CI95%=1.2;5.9, p=0.02). Among the 26 HCWs with a SARS-CoV-2-positive nasopharyngeal swab, 7 (26.9%) had no symptom at the time of the RT-PCR positivity. Conclusions: The proportion of HCWs with confirmed or possible SARS-CoV-2 infection was high. There were less occurrences of high-risk exposure with patients than with colleagues, but those were associated with an increased risk of infection.

SARS-CoV-2 N-antigenemia: A new alternative to nucleic acid amplification techniques (preprint)

Background. Molecular assays on nasopharyngeal swabs remain the cornerstone of COVID-19 diagnostic. Despite massive worldwide efforts, the high technicalities of nasopharyngeal sampling and molecular assays, as well as scarce resources of reagents, limit our testing capabilities. Several strategies failed, to date, to fully alleviate this testing process (e.g. saliva sampling or antigen testing on nasopharyngeal samples). We assessed the performances of a new ELISA microplate assay quantifying SARS-CoV-2 nucleocapsid antigen (N-antigen) in serum or plasma. Methods. The specificity of the assay, determined on 63 non-COVID patients, was 98.4% (95% confidence interval [CI], 85.3 to 100). Performances were determined on 227 serum samples from 165 patients with RT-PCR confirmed SARS-CoV-2 infection included in the French COVID and CoV-CONTACT cohorts. Findings. Sensitivity was 132/142, 93.0% (95% CI, 84.7 to 100), within the first two weeks after symptoms onset. A subset of 73 COVID-19 patients had a serum collected within 24 hours following or preceding a positive nasopharyngeal swab. Among patients with high nasopharyngeal viral loads, Ct value below 30 and 33, only 1/50 and 4/67 tested negative for N-antigenemia, respectively. Among patients with a negative nasopharyngeal RT-PCR, 8/12 presented positive N-antigenemia. The lower respiratory tract was explored for 6/8 patients, showing positive PCR in 5 cases. Interpretation. This is the first demonstration of the N-antigen antigenemia during COVID-19. Its detection presented a robust sensitivity, especially within the first 14 days after symptoms onset and high nasopharyngeal viral loads. These findings have to be confirmed with higher representation of outpatients. This approach could provide a valuable new option for COVID-19 diagnosis, only requiring a blood draw and easily scalable in all clinical laboratories.

Outcome of SARS-CoV-2 infection linked to MAIT cell activation and cytotoxicity: evidence for an IL-18 dependent mechanism (preprint)

Immune system dysfunction is paramount in Coronavirus disease 2019 (COVID-19) severity and fatality rate. Mucosal-Associated Invariant T (MAIT) cells are innate-like T cells involved in mucosal immunity and protection against viral infections. Here, we studied the immune cell landscape, with emphasis on MAIT cells, in a cohort of 182 patients including patients at various stages of disease activity. A profound decrease of MAIT cell counts in blood of critically ill patients was observed. These cells showed a strongly activated and cytotoxic phenotype that positively correlated with circulating pro-inflammatory cytokines, notably IL-18. MAIT cell alterations markedly correlated with disease severity and patient mortality. SARS-CoV-2-infected macrophages activated MAIT cells in a cytokine-dependent manner involving an IFN-dependent early phase and an IL-18-induced later phase. Therefore, altered MAIT cell phenotypes represent valuable biomarkers of disease severity and their therapeutic manipulation might prevent the inflammatory phase involved in COVID-19 aggravation.

Emergency calls are early indicators of ICU bed requirement during the COVID-19 epidemic A retrospective study in Ile-de-France region, France (preprint)

Background: The aim of our retrospective study was to evaluate the earliest COVID19-related signal to anticipate requirements of intensive care unit (ICU) beds. Although the number of ICU beds is crucial during the COVID-19 epidemic, there is no recognized early indicator to anticipate it. Methods: In the Ile-de-France region, from February 20 to May 5, 2020, emergency medical service (EMS) calls and the response provided (ambulances) together the percentage of positive reverse transcriptase polymerase chain reaction (RT-PCR) tests, general practitioner (GP) and emergency department (ED) visits, and hospital admissions of COVID-19 patients were recorded daily and compared to the number of ICU patients. Correlation curve analysis was performed to determine the best correlation coefficient, depending on the number of days the indicator has been shifted. Primary endpoint was the number of ICU patients. Results: EMS calls, percentage of positive RT-PCR tests, ambulances used, ED and GP visits of COVID-19 patients were strongly associated with COVID-19 ICU patients with an anticipation delay of 23, 15, 14, 13, and 12 days respectively. Hospitalization did not anticipate ICU bed requirement. Conclusion: The daily number of COVID19-related telephone calls received by the EMS and corresponding dispatch ambulances, and the proportion of positive RT-PCR tests were the earliest indicators of the number of COVID19 patients requiring ICU care during the epidemic crisis, rapidly followed by ED and GP visits. This information may help health authorities to anticipate a future epidemic, including a second wave of COVID19 or decide additional social measures.

Multicenter comparison of the Cobas 6800 system with the RealStar RT-PCR kit for the detection of SARS-CoV-2 (preprint)

BackgroundRT-PCR testing is crucial in the diagnostic of SARS-CoV-2 infection. The use of reliable and comparable PCR assays is a cornerstone to allow use of different PCR assays depending on the local equipment. In this work, we provide a comparison of the Cobas(R) (Roche) and the RealStar(R) assay (Altona). MethodsAssessment of the two assays was performed prospectively in three reference Parisians hospitals, using 170 clinical samples. They were tested with the Cobas(R) assay, selected to obtain a distribution of cycle threshold (Ct) as large as possible, and tested with the RealStar assay with three largely available extraction platforms: QIAsymphony (Qiagen), MagNAPure (Roche) and NucliSENS-easyMag (BioMerieux). ResultsOverall, the agreement (positive for at least one gene) was 76%. This rate differed considerably depending on the Cobas Ct values for gene E: below 35 (n = 91), the concordance was 99%. Regarding the positive Ct values, linear regression analysis showed a determination correlation (R2) of 0.88 and the Deming regression line revealed a strong correlation with a slope of 1.023 and an intercept of -3.9. Bland-Altman analysis showed that the mean difference (Cobas(R) minus RealStar(R)) was + 3.3 Ct, with a SD of + 2.3 Ct. ConclusionsIn this comparison, both RealStar(R) and Cobas(R) assays provided comparable qualitative results and a high correlation when both tests were positive. Discrepancies exist after 35 Ct and varied depending on the extraction system used for the RealStar(R) assay, probably due to a low viral load close to the detection limit of both assays.

SARS-CoV-2 serological analysis of COVID-19 hospitalized patients, pauci-symptomatic individuals and blood donors. (preprint)

It is of paramount importance to evaluate the prevalence of both asymptomatic and symptomatic cases of SARS-CoV-2 infection and their antibody response profile. Here, we performed a pilot study to assess the levels of anti-SARS-CoV-2 antibodies in samples taken from 491 pre- epidemic individuals, 51 patients from Hopital Bichat (Paris), 209 pauci-symptomatic individuals in the French Oise region and 200 contemporary Oise blood donors. Two in-house ELISA assays, that recognize the full-length nucleoprotein (N) or trimeric Spike (S) ectodomain were implemented. We also developed two novel assays: the S-Flow assay, which is based on the recognition of S at the cell surface by flow-cytometry, and the LIPS assay that recognizes diverse antigens (including S1 or N C- terminal domain) by immunoprecipitation. Overall, the results obtained with the four assays were similar, with differences in sensitivity that can be attributed to the technique and the antigen in use. High antibody titers were associated with neutralisation activity, assessed using infectious SARS-CoV- 2 or lentiviral-S pseudotypes. In hospitalized patients, seroconversion and neutralisation occurred on 5-14 days post symptom onset, confirming previous studies. Seropositivity was detected in 29% of pauci-symptomatic individuals within 15 days post-symptoms and 3 % of blood of healthy donors collected in the area of a cluster of COVID cases. Altogether, our assays allow for a broad evaluation of SARS-CoV2 seroprevalence and antibody profiling in different population subsets.

SARS-CoV-2 specific antibody responses in COVID-19 patients (preprint)

A new coronavirus, SARS-CoV-2, has recently emerged to cause a human pandemic. Whereas molecular diagnostic tests were rapidly developed, serologic assays are still lacking, yet urgently needed. Validated serologic assays are important for contact tracing, identifying the viral reservoir and epidemiological studies. Here, we developed serological assays for the detection of SARS-CoV-2 neutralizing, spike- and nucleocapsid-specific antibodies. Using serum samples from patients with PCR-confirmed infections of SARS-CoV-2, other coronaviruses, or other respiratory pathogenic infections, we validated and tested various antigens in different in-house and commercial ELISAs. We demonstrate that most PCR-confirmed SARS-CoV-2 infected individuals seroconverted, as revealed by sensitive and specific in-house ELISAs. We found that commercial S1 IgG or IgA ELISAs were of lower specificity while sensitivity varied between the two, with IgA showing higher sensitivity. Overall, the validated assays described here can be instrumental for the detection of SARS-CoV-2-specific antibodies for diagnostic, seroepidemiological and vaccine evaluation studies.