SARS-CoV-2 immunoassays in a predominantly vaccinated population: Performances and qualitative agreements obtained with two analytical approaches and four immunoassays.

BACKGROUND AND OBJECTIVES: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serosurveys are typically analysed by applying a fixed threshold for seropositivity ('conventional approach'). However, this approach underestimates the seroprevalence of anti-nucleocapsid (N) in vaccinated individuals-who often exhibit a difficult-to-detect anti-N response. This limitation is compounded by delays between the onset of infection and sample collection. To address this issue, we compared the performance of four immunoassays using a new analytical approach ('ratio-based approach'), which determines seropositivity based on an increase in anti-N levels. MATERIALS AND METHODS: Two groups of plasma donors and four immunoassays (Elecsys total anti-N, VITROS total anti-N, Architect anti-N Immunoglobulin G (IgG) and in-house total anti-N) were evaluated. First-group donors (N = 145) had one positive SARS-CoV-2 polymerase chain reaction (PCR) test result and had made two plasma donations, including one before and one after the PCR test (median = 27 days post-PCR). Second-group donors (N = 100) had made two plasma donations early in the Omicron wave. RESULTS: Among first-group donors (97.9% vaccinated), sensitivity estimates ranged from 60.0% to 89.0% with the conventional approach, compared with 94.5% to 98.6% with the ratio-based approach. Among second-group donors, Fleiss's κ ranged from 0.56 to 0.83 with the conventional approach, compared with 0.90 to 1.00 with the ratio-based approach. CONCLUSION: With the conventional approach, the sensitivity of four immunoassays-measured in a predominantly vaccinated population based on samples collected ~1 month after a positive test result-fell below regulatory agencies requirement of ≥95%. The ratio-based approach significantly improved the sensitivities and qualitative agreement among immunoassays, to the point where all would meet this requirement.

Quality of life and cost-effectiveness of convalescent plasma compared to standard care for hospitalized COVID-19 patients in the CONCOR-1 trial.

BACKGROUND: The CONvalescent Plasma for Hospitalized Adults With COVID-19 Respiratory Illness (CONCOR-1) trial was a multicenter randomized controlled trial assessing convalescent plasma in hospitalized COVID-19 patients. This study evaluates the cost-effectiveness of convalescent plasma and its impact on quality-of-life to provide insight into its potential as an alternative treatment in resource-constrained settings. METHODS: Individual patient data on health outcomes and resource utilization from the CONCOR-1 trial were used to conduct the analysis from the Canadian public payer's perspective with a time horizon of 30 days post-randomization. Baseline and 30-day EQ-5D-5L were measured to calculate quality-adjusted survival. All costs are presented in 2021 Canadian dollars. The base case assessed the EQ-5D-5L scores of hospitalized inpatients reporting at both timepoints, and a utility score of 0 was assigned for patients who died within 30 days. Costs for all patients enrolled were used. The sensitivity analysis utilizes EQ-5D-5L scores from the same population but only uses costs from this population. RESULTS: 940 patients were randomized: 627 received CCP and 313 received standard care. The total costs were $28,716 (standard deviation, $25,380) and $24,258 ($22,939) for the convalescent plasma and standard care arms respectively. EQ-5D-5L scores were 0.61 in both arms (p = .85) at baseline. At 30 days, EQ-5D-5L scores were 0.63 and 0.64 for patients in the convalescent plasma and standard care arms, respectively (p = .46). The incremental cost was $4458 and the incremental quality-adjusted life day was -0.078. DISCUSSION: Convalescent plasma was less effective and more costly than standard care in treating hospitalized COVID-19.

Bioluminescence imaging reveals enhanced SARS-CoV-2 clearance in mice with combinatorial regimens.

Direct acting antivirals (DAAs) represent critical tools for combating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) that have escaped vaccine-elicited spike-based immunity and future coronaviruses with pandemic potential. Here, we used bioluminescence imaging to evaluate therapeutic efficacy of DAAs that target SARS-CoV-2 RNA-dependent RNA polymerase (favipiravir, molnupiravir) or main protease (nirmatrelvir) against Delta or Omicron VOCs in K18-hACE2 mice. Nirmatrelvir displayed the best efficacy followed by molnupiravir and favipiravir in suppressing viral loads in the lung. Unlike neutralizing antibody treatment, DAA monotherapy regimens did not eradicate SARS-CoV-2 in mice, but combining molnupiravir with nirmatrelvir exhibited superior additive efficacy and led to virus clearance. Furthermore, combining molnupiravir with caspase-1/4 inhibitor mitigated inflammation and lung pathology whereas combining molnupiravir with COVID-19 convalescent plasma demonstrated synergy, rapid virus clearance, and 100% survival. Thus, our study provides insights into in vivo treatment efficacies of DAAs and other effective combinations to bolster COVID-19 therapeutic arsenal.

Risk factors for T-cell lymphopenia in frequent platelet donors: The BEST collaborative study.

BACKGROUND: Severe T-cell lymphopenia of uncertain clinical significance has been observed in frequent apheresis platelet donors. Two commonly used plateletpheresis instruments are the Trima Accel, which uses a leukoreduction system (LRS) chamber to trap leukocytes and the Fenwal Amicus, which does not use an LRS chamber. STUDY DESIGN AND METHODS: We performed an international, multicenter, observational study comparing T-cell populations in frequent platelet donors collected exclusively using the Trima instrument (n = 131) or the Amicus instrument (n = 77). Age- and sex-matched whole blood donors (n = 126) served as controls. RESULTS: CD4+ T-cell counts <200 cells/µL were found in 9.9% of frequent Trima (LRS+) platelet donors, 4.4% of frequent Amicus (LRS-) platelet donors, and 0 whole blood donors (p < .0001). CD4+ T-cell counts <200 cells/µL were only seen in platelet donors with ≥200 lifetime donations. In multivariable analysis, age, lifetime donations, and instrument (Trima vs. Amicus) were independent risk factors for lymphopenia. In 40 Trima platelet donors, a plasma rinseback procedure was routinely performed following platelet collections. No Trima platelet donors receiving plasma rinseback had a CD4+ T-cell count <200 cells/µL versus 13/91 Trima platelet donors not receiving plasma rinseback (p = .01). DISCUSSION: Recurrent bulk lymphocyte removal appears to contribute to the development of T-cell lymphopenia in frequent, long-term platelet donors. Lymphopenia is more common when an LRS chamber is used during platelet collection but can occur without an LRS chamber. Blood centers using LRS chambers can mitigate donor lymphopenia by performing plasma rinseback.

Humoral Responses Elicited after a Fifth Dose of SARS-CoV-2 mRNA Bivalent Vaccine.

While an important part of the world's population is vaccinated against SARS-CoV-2, new variants continue to emerge. We observe that even after a fifth dose of the mRNA bivalent vaccine, most vaccinated individuals have antibodies that poorly neutralize several Omicron subvariants, including BQ.1.1, XBB, XBB.1.5, FD.1.1, and CH.1.1. However, Fc-effector functions remain strong and stable over time against new variants, which may partially explain why vaccines continue to be effective. We also observe that donors who have been recently infected have stronger antibody functional activities, including neutralization and Fc-effector functions, supporting the observations that hybrid immunity leads to better humoral responses.

Combinatorial Regimens Augment Drug Monotherapy for SARS-CoV-2 Clearance in Mice.

Direct acting antivirals (DAAs) represent critical tools for combating SARS-CoV-2 variants of concern (VOCs) that evolve to escape spike-based immunity and future coronaviruses with pandemic potential. Here, we used bioluminescence imaging to evaluate therapeutic efficacy of DAAs that target SARS-CoV-2 RNA-dependent RNA polymerase (favipiravir, molnupiravir) or Main protease (nirmatrelvir) against Delta or Omicron VOCs in K18-hACE2 mice. Nirmatrelvir displayed the best efficacy followed by molnupiravir and favipiravir in suppressing viral loads in the lung. Unlike neutralizing antibody treatment, DAA monotherapy did not eliminate SARS-CoV-2 in mice. However, targeting two viral enzymes by combining molnupiravir with nirmatrelvir resulted in superior efficacy and virus clearance. Furthermore, combining molnupiravir with Caspase-1/4 inhibitor mitigated inflammation and lung pathology whereas combining molnupiravir with COVID-19 convalescent plasma yielded rapid virus clearance and 100% survival. Thus, our study provides insights into treatment efficacies of DAAs and other effective combinations to bolster COVID-19 therapeutic arsenal.

A Recent SARS-CoV-2 Infection Enhances Antibody-Dependent Cellular Cytotoxicity against Several Omicron Subvariants following a Fourth mRNA Vaccine Dose.

Since the beginning of the SARS-CoV-2 pandemic, several variants of concern (VOCs), such as the Alpha, Beta, Gamma, Delta and Omicron variants, have arisen and spread worldwide. Today, the predominant circulating subvariants are sublineages of the Omicron variant, which have more than 30 mutations in their Spike glycoprotein compared to the ancestral strain. The Omicron subvariants were significantly less recognized and neutralized by antibodies from vaccinated individuals. This resulted in a surge in the number of infections, and booster shots were recommended to improve responses against these variants. While most studies mainly measured the neutralizing activity against variants, we and others previously reported that Fc-effector functions, including antibody-dependent cellular cytotoxicity (ADCC), play an important role in humoral responses against SARS-CoV-2. In this study, we analyzed Spike recognition and ADCC activity against several Omicron subvariants by generating cell lines expressing different Omicron subvariant Spikes. We tested these responses in a cohort of donors, who were recently infected or not, before and after a fourth dose of mRNA vaccine. We showed that ADCC activity is less affected than neutralization by the antigenic shift of the tested Omicron subvariant Spikes. Moreover, we found that individuals with a history of recent infection have higher antibody binding and ADCC activity against all Omicron subvariants than people who were not recently infected. With an increase in the number of reinfections, this study helps better understand Fc-effector responses in the context of hybrid immunity.

Evaluation of anti-nucleocapsid level variation to assess SARS-CoV-2 seroprevalence in a vaccinated population.

BACKGROUND: Serosurveys have been key to public health decision-making since the beginning of the SARS-CoV-2 pandemic. However, several studies have uncovered that vaccination blunts the anti-nucleocapsid (N) response to a subsequent infection, which hinders the ability of serologic assays (including commercial ones) to detect recent infections. We therefore developed a new analytical approach to increase the sensitivity of detection of infection in vaccinated individuals. METHODS: Two samples were obtained from 248 SARS-CoV-2-positive (PCR-confirmed), vaccinated donors: one before the infection (reference sample) and one after (test sample). All samples were tested using an in-house, anti-N enzyme-linked immunosorbent assay (ELISA) which had a sensitivity of 98.1% before the mass vaccination campaign. Instead of applying a seropositivity threshold based on a single absorbance value (i.e. conventional approach), seropositivity was determined based on the ratio between the anti-N absorbance of the test and reference samples. RESULTS: The sensitivity of the new approach to detect infection in vaccinated individuals was 95.2% using a cut-off of 1.5 for the anti-N ratio, whereas that of the conventional approach was 63.3%. CONCLUSION: The new analytical approach described herein captured a significantly greater proportion of vaccinated individuals with a known history of SARS-CoV-2 infection than the conventional approach used in most serosurveys.

Humoral Responses against BQ.1.1 Elicited after Breakthrough Infection and SARS-CoV-2 mRNA Vaccination.

The Omicron BQ.1.1 variant is now the major SARS-CoV-2 circulating strain in many countries. Because of the many mutations present in its Spike glycoprotein, this variant is resistant to humoral responses elicited by monovalent mRNA vaccines. With the goal to improve immune responses against Omicron subvariants, bivalent mRNA vaccines have recently been approved in several countries. In this study, we measure the capacity of plasma from vaccinated individuals, before and after a fourth dose of mono- or bivalent mRNA vaccine, to recognize and neutralize the ancestral (D614G) and the BQ.1.1 Spikes. Before and after the fourth dose, we observe a significantly better recognition and neutralization of the ancestral Spike. We also observe that fourth-dose vaccinated individuals who have been recently infected better recognize and neutralize the BQ.1.1 Spike, independently of the mRNA vaccine used, than donors who have never been infected or have an older infection. Our study supports that hybrid immunity, generated by vaccination and a recent infection, induces higher humoral responses than vaccination alone, independently of the mRNA vaccine used.

Cohort profile: A Québec-based plasma donor biobank to study COVID-19 immunity (PlasCoV).

PURPOSE: The long-term humoral immunity to COVID-19 is not well understood owing to the continuous emergence of new variants of concern, the evolving vaccine-induced and infection-induced immunity, and the limited duration of follow-up in previous studies. As the sole blood service in Québec (Canada), Héma-Québec established a COVID-19-focused biobank ('PlasCoV') in April 2021. PARTICIPANTS: As of January 2022, the biobank included 86 483 plasma samples from 15 502 regular donors (age range=18-84 years, females=49.7%), for an average of 5.6 donations per donor. Nearly two-thirds (65.6%) of biobank donors made at least two donations, with many donors having provided samples prevaccination and postvaccination (3061 (19.7%)) or preinfection and postinfection (131 (0.8%)), thus allowing for longitudinal studies on vaccine-induced and infection-induced immunity. FINDINGS TO DATE: A study that used PlasCoV samples revealed that previously infected individuals who received a single dose of the BNT162b2 COVID-19 vaccine exhibited the strongest immune response. By contrast, SARS-CoV-2-naïve individuals required two vaccine doses to produce a maximal immune response. Furthermore, the results of a four-phase seroprevalence study indicated that the antinucleocapsid (N) response wanes rapidly, so that up to one-third of previously infected donors were seronegative for anti-N. FUTURE PLANS: Donations from individuals who consented to participate before 1 October 2022 will be collected up until 31 March 2023. This plasma biobank will facilitate the conduct of longitudinal studies on COVID-19 immunity, thus helping to provide valuable insights into the anti-SARS-CoV-2 immune response and its persistence, and the effects of vaccination and variants on the specificity of the anti-SARS-CoV-2 immune response.

Spike recognition and neutralization of SARS-CoV-2 Omicron subvariants elicited after the third dose of mRNA vaccine.

Several severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron subvariants have recently emerged, becoming the dominant circulating strains in many countries. These variants contain a large number of mutations in their spike glycoprotein, raising concerns about vaccine efficacy. In this study, we evaluate the ability of plasma from a cohort of individuals that received three doses of mRNA vaccine to recognize and neutralize these Omicron subvariant spikes. We observed that BA.4/5 and BQ.1.1 spikes are markedly less recognized and neutralized compared with the D614G and other Omicron subvariant spikes tested. Also, individuals who have been infected before or after vaccination present better humoral responses than SARS-CoV-2-naive vaccinated individuals, thus indicating that hybrid immunity generates better humoral responses against these subvariants.

The Fc-effector function of COVID-19 convalescent plasma contributes to SARS-CoV-2 treatment efficacy in mice.

COVID-19 convalescent plasmas (CCPs) are chosen for plasma therapy based on neutralizing titers and anti-Spike immunoglobulin levels. However, CCP characteristics that promote SARS-CoV-2 control are complex and incompletely defined. Using an in vivo imaging approach, we demonstrate that CCPs with low neutralizing (ID50 ≤ 1:250), but moderate to high Fc-effector activity, in contrast to those with poor Fc function, delay mortality and/or improve survival of SARS-CoV-2-challenged K18-hACE2 mice. The impact of innate immune cells on CCP efficacy depended on their residual neutralizing activity. Fractionation of a selected CCP revealed that IgG and Ig(M + A) were required during therapy, but the IgG fraction alone sufficed during prophylaxis. Finally, despite reduced neutralization, ancestral SARS-CoV-2-elicited CCPs significantly delayed Delta and Beta-induced mortality suggesting that Fc-effector functions contribute to immunity against VOCs. Thus, Fc activity of CCPs provide a second line of defense when neutralization is compromised and can serve as an important criterion for CCP selection.

Assessment of the soluble proteins HMGB1, CD40L and CD62P during various platelet preparation processes and the storage of platelet concentrates: The BEST collaborative study.

BACKGROUND: Structural and biochemical changes in stored platelets are influenced by collection and processing methods. This international study investigates the effects of platelet (PLT) processing and storage conditions on HMGB1, sCD40L, and sCD62P protein levels in platelet concentrate supernatants (PCs). STUDY DESIGN/METHODS: PC supernatants (n = 3748) were collected by each international centre using identical centrifugation methods (n = 9) and tested centrally using the ELISA/Luminex platform. Apheresis versus the buffy coat (BC-PC) method, plasma storage versus PAS and RT storage versus cold (4°C) were investigated. We focused on PC preparation collecting samples during early (RT: day 1-3; cold: day 1-5) and late (RT: day 4-7; cold: day 7-10) storage time points. RESULTS: HMGB1, sCD40L, and sCD62P concentrations were similar during early storage periods, regardless of storage solution (BC-PC plasma and BC-PC PAS-E) or temperature. During storage and without PAS, sCD40L and CD62P in BC-PC supernatants increased significantly (+33% and +41%, respectively) depending on storage temperature (22 vs. 4°C). However, without PAS-E, levels decreased significantly (-31% and -20%, respectively), depending on storage temperature (22 vs. 4°C). Contrastingly, the processing method appeared to have greater impact on HMGB1 release versus storage duration. These data highlight increases in these parameters during storage and differences between preparation methods and storage temperatures. CONCLUSIONS: The HMGB1 release mechanism/intracellular pathways appear to differ from sCD62P and sCD40L. The extent to which these differences affect patient outcomes, particularly post-transfusion platelet increment and adverse events, warrants further investigation in clinical trials with various therapeutic indications.

A boost with SARS-CoV-2 BNT162b2 mRNA vaccine elicits strong humoral responses independently of the interval between the first two doses.

Due to the recrudescence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections worldwide, mainly caused by the Omicron variant of concern (VOC) and its sub-lineages, several jurisdictions are administering an mRNA vaccine boost. Here, we analyze humoral responses induced after the second and third doses of an mRNA vaccine in naive and previously infected donors who received their second dose with an extended 16-week interval. We observe that the extended interval elicits robust humoral responses against VOCs, but this response is significantly diminished 4 months after the second dose. Administering a boost to these individuals brings back the humoral responses to the same levels obtained after the extended second dose. Interestingly, we observe that administering a boost to individuals that initially received a short 3- to 4-week regimen elicits humoral responses similar to those observed in the long interval regimen. Nevertheless, humoral responses elicited by the boost in naive individuals do not reach those present in previously infected vaccinated individuals.

Blood Endothelial-Cell Extracellular Vesicles as Potential Biomarkers for the Selection of Plasma in COVID-19 Convalescent Plasma Therapy.

Despite the advancement of vaccination and therapies currently available, deaths due to the coronavirus disease 2019 (COVID-19) are still heavily documented. Severely infected individuals experience a generalized inflammatory storm, caused by massive secretion of pro-inflammatory cytokines that can lead to endothelial dysfunction, cardiovascular disease, multi-organ failure, and even death. COVID-19 convalescent plasma (CCP) therapy, selected primarily based on anti-SARS-CoV-2 antibody levels, has not been as convincing as expected in the fight against COVID-19. Given the consequences of a dysfunctional endothelium on the progression of the disease, we propose that the selection of plasma for CCP therapy should be based on more specific parameters that take into consideration the effect on vascular inflammation. Thus, in the present study, we have characterized a subset of CCP that have been used for CCP therapy and measured their anti- or pro-inflammatory effect on human coronary artery endothelial cells (HCAECs). Our data revealed that the longer the time lapse between the onset of symptoms and the plasma donation, the more mitochondrial dysfunction can be evidenced. The concentration of blood endothelial cell extracellular vesicles (BEC-EVs) was increased in the plasma of young individuals with mild symptoms. This type of selected convalescent plasma promoted the activation of the blood vascular endothelium, as reflected by the overexpression of ICAM1 and NFκB1 and the downregulation of VE-Cadherin. We propose this mechanism is a warning signal sent by the injured endothelium to trigger self-defense of peripheral blood vessels against excessive inflammation. Therefore, these results are in line with our previous data. They suggest that a more specific selection of COVID-19 convalescent plasma should be based on the time of donation following the onset of the clinical symptoms of the donor, the severity of the symptoms, and the age of the donor. These characteristics are relatively easy to identify in any hospital and would reflect the concentration of plasma BEC-EVs and be optimal in CCP therapy.

COVID-19 vaccine humoral response in frequent platelet donors with plateletpheresis-associated lymphopenia.

BACKGROUND: Plateletpheresis involves platelet separation and collection from whole blood while other blood cells are returned to the donor. Because platelets are replaced faster than red blood cells, as many as 24 donations can be done annually. However, some frequent apheresis platelet donors (>20 donations annually) display severe plateletpheresis-associated lymphopenia; in particular, CD4+ T but not B cell numbers are decreased. COVID-19 vaccination thereby provides a model to assess whether lymphopenic platelet donors present compromised humoral immune responses. STUDY DESIGN AND METHODS: We assessed vaccine responses following 2 doses of COVID-19 vaccination in a cohort of 43 plateletpheresis donors with a range of pre-vaccination CD4+ T cell counts (76-1537 cells/µl). In addition to baseline T cell measurements, antibody binding assays to full-length Spike and the Receptor Binding Domain (RBD) were performed pre- and post-vaccination. Furthermore, pseudo-particle neutralization and antibody-dependent cellular cytotoxicity assays were conducted to measure antibody functionality. RESULTS: Participants were stratified into two groups: <400 CD4/µl (n = 27) and ≥ 400 CD4/µl (n = 16). Following the first dose, 79% seroconverted within the <400 CD4/µl group compared to 87% in the ≥400 CD4/µl group; all donors were seropositive post-second dose with significant increases in antibody levels. Importantly differences in CD4+ T cell levels minimally impacted neutralization, Spike recognition, and IgG Fc-mediated effector functions. DISCUSSION: Overall, our results indicate that lymphopenic plateletpheresis donors do not exhibit significant immune dysfunction; they have retained the T and B cell functionality necessary for potent antibody responses after vaccination.

Humoral immune responses against SARS-CoV-2 Spike variants after mRNA vaccination in solid organ transplant recipients.

Although SARS-CoV-2 mRNA vaccination has been shown to be safe and effective in the general population, immunocompromised solid organ transplant recipients (SOTRs) were reported to have impaired immune responses after one or two doses of vaccine. In this study, we examined humoral responses induced after the second and the third dose of mRNA vaccine in different SOTR (kidney, liver, lung, and heart). Compared to a cohort of SARS-CoV-2 naïve immunocompetent health care workers (HCWs), the second dose induced weak humoral responses in SOTRs, except for the liver recipients. The third dose boosted these responses but they did not reach the same level as in HCW. Interestingly, although the neutralizing activity against Delta and Omicron variants remained very low after the third dose, Fc-mediated effector functions in SOTR reached similar levels as in the HCW cohort. Whether these responses will suffice to protect SOTR from severe outcome remains to be determined.

Production and Quality Assurance of Human Polyclonal Hyperimmune Immunoglobulins Against SARS-CoV-2.

The coronavirus disease 2019 (COVID-19) pandemic has highlighted the potential therapeutic value of early passive polyclonal immunotherapy using high-titer convalescent plasma (CCP). Human polyclonal hyperimmune immunoglobulin (HIG) has several advantages over CCP. Unlike CCP, HIG can provide standardized and controlled antibody content. It is also subjected to robust pathogen reduction rendering it virally safe and is purified by technologies demonstrated to preserve immunoglobulin neutralization capacity and Fc fragment integrity. This document provides an overview of current practices and guidance for the collection and testing of plasma rich in antibodies against Severe Acute Respiratory Coronavirus 2 (SARS-CoV-2) and its industrial fractionation for the manufacture of quality-assured and safe HIG. Considerations are also given to the production of HIG preparations in low- and middle-income countries.

Multicenter evaluation of the IL-3-pSTAT5 assay to assess the potency of cryopreserved stem cells from cord blood units: The BEST Collaborative study.

BACKGROUND: The IL-3-pSTAT5 assay, a new, rapid, and standardized flow-cytometry-based assay may compensate for several limitations of the colony-forming unit (CFU) assay typically used for stem cell potency assessments of cord blood units (CBU). We performed an inter-laboratory evaluation of the performance of this new assay. STUDY DESIGN AND METHODS: This Biomedical Excellence for Safer Transfusion (BEST) Collaborative multicenter, international study included 15 participants from public cord blood banks (CBBs), CBB-supporting research laboratories, and stem cell laboratories. To perform the IL-3-pSTAT5 assay, participating centers received reagents, instructions, and 10 blind CBU samples, including eight normal samples and two samples exposed to a transient warming event. We measured inter-laboratory agreement qualitatively (proportion of correctly classified samples) and quantitatively (coefficient of variation [CV], correlation coefficients, receiver operating characteristics (ROC) curve, and intraclass correlation coefficient [ICC]). RESULTS: The qualitative agreement was 97.3% (i.e., 107/110; Fleiss' kappa = 0.835). The average CV on a per-sample basis was 11.57% among all samples, 8.99% among normal samples, and on a per-center basis was 9.42% among normal samples. In a correlation matrix that compared results across centers, the mean Pearson's correlation coefficient was 0.88 (standard deviation = 0.04). The ICC was 0.83 (95% confidence interval = 0.68-0.95). The area under the curve (AUC) from the ROC curve was 0.9974. DISCUSSION: Excellent qualitative and quantitative agreement was exhibited across laboratories. The IL-3-pSTAT5 assay may therefore be implemented in flow cytometry laboratories to rapidly and reliably provide standardized measures of stem cell potency in CBUs.

Seroprevalence of SARS-CoV-2 antibodies among blood donors in Québec: an update from a serial cross-sectional study.

OBJECTIVES: We previously estimated the seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies following the first pandemic wave at 2.23% in Québec, Canada. Following the much bigger second wave in fall 2020 and early 2021, we estimated the seroprevalence of anti-SARS-CoV-2 in Québec during the first months of 2021. METHODS: Blood samples from regular, asymptomatic (for ≥ 14 days) donors were collected between January 25, 2021 and March 11, 2021. Anti-SARS-CoV-2 seropositivity was assessed using an enzyme-linked immunosorbent assay that captures antibodies directed against the receptor binding domain of the SARS-CoV-2 spike (and hence cannot discriminate between infection- and vaccine-induced seropositivity). Seroprevalence estimates were adjusted for regional distribution, age, and sex. RESULTS: Samples from 7924 eligible donors were analyzed, including 620 (7.8%) vaccinated donors and 7046 (88.9%) unvaccinated donors (vaccination status unknown for 258 (3.3%) donors). Overall, median age was 51 years; 46.4% of donors were female. The adjusted seroprevalence was 10.5% (95% CI = 9.7-11.3) in the unvaccinated population and 14.7% (95% CI = 13.8-15.6) in the overall population. Seroprevalence gradually decreased with age and was higher among donors who self-identified as having a racial/ethnic background other than white, both in the overall and in the unvaccinated populations. CONCLUSION: The seroprevalence of SARS-CoV-2 antibodies significantly increased in Québec since spring 2020, with younger persons and ethnic minorities being disproportionately affected. When compared with the cumulative incidence rate reported by public health authorities (i.e., 3.3% as of March 11, 2021), these results suggest that a substantial proportion of infections remain undetected despite improvements in access to COVID-19 testing.

RéSUMé: OBJECTIFS: Lors d'une première étude, nous avons estimé la séroprévalence des anticorps contre le syndrome respiratoire aigu sévère coronavirus 2 (SRAS-CoV-2) après la première vague pandémique à 2,23 % au Québec, Canada. Cette seconde étude estime la séroprévalence de l'anti-SRAS-CoV-2 au Québec lors de la deuxième vague pandémique. MéTHODES: Des échantillons de donneurs de sang asymptomatiques (≥ 14 jours) ont été prélevés entre le 25 janvier et le 11 mars 2021. La séropositivité a été évaluée à l'aide d'un dosage immuno-enzymatique qui capture les anticorps dirigés contre la protéine Spike du récepteur de domaine de liaison du SARS-CoV-2 (et ne peut donc distinguer l'immunité induite par l'infection et la vaccination). La séroprévalence a été ajustée en fonction de l'âge et du sexe par région. RéSULTATS: Des échantillons de 7 924 donneurs ont été analysés, dont 620 (7,8 %) étaient vaccinés et 7 046 (88,9 %) étaient non vaccinés (statut vaccinal inconnu pour 258 (3,3 %) donneurs). Dans l'ensemble, l'âge médian était de 51 ans et 46,4 % des donneurs étaient des femmes. La séroprévalence ajustée était de 10,5 % (IC 95 % = 9,7 à 11,3) dans la population non vaccinée et de 14,7 % (IC 95 % = 13,8 à 15,6) dans la population globale. La séroprévalence diminuait progressivement avec l'âge et était plus élevée chez les donneurs d'origine ethnique autre que blanche. CONCLUSION: La séroprévalence anti-SRAS-CoV-2 a considérablement augmenté au Québec depuis le printemps 2020, les personnes plus jeunes et les minorités ethniques étant plus touchées. Comparés au taux d'incidence cumulatif signalé par la santé publique (c.-à-d. 3,3 % au 11 mars 2021), ces résultats suggèrent qu'une proportion importante d'infections reste non détectée.