Omicron Breakthrough Infection Elicits Superior Humoral and Mucosal Immune Responses to SARS-CoV-2 Variants than an Intramuscular Booster Dose (preprint)

Our understanding of the quality of cellular and humoral immunity conferred by COVID-19 vaccination alone versus vaccination plus SARS-CoV-2 breakthrough (BT) infection remains incomplete. While the current (2023) SARS-CoV-2 immune landscape of Canadians is complex, in late 2021 most Canadians had either just received a third dose of COVID-19 vaccine, or had received their two dose primary series and then experienced an Omicron BT. Herein we took advantage of this coincident timing to contrast cellular and humoral immunity conferred by three doses of vaccine versus two doses plus BT. Our results show that mild BT infection induces cell-mediated immune responses to variants comparable to an intramuscular vaccine booster dose. In contrast, BT subjects had higher salivary IgG and IgA levels against the Omicron Spike and enhanced reactivity to the ancestral Spike for the IgA isotype, which also reacted with SARS-CoV-1. Serum neutralizing antibody levels against the ancestral strain and the variants were also higher after BT infection. Our results support the need for mucosal vaccines to emulate the enhanced mucosal and humoral immunity induced by Omicron without exposing individuals to the risks associated with SARS-CoV-2 infection.

Natural Language Processing for Clinical Laboratory Data Repository Systems: Implementation and Evaluation for Respiratory Viruses (preprint)

Background With the growing volume and complexity of laboratory repositories, it has become tedious to parse unstructured data into structured and tabulated formats for secondary uses such as decision support, quality assurance, and outcome analysis. However, advances in Natural Language Processing (NLP) approaches have enabled efficient and automated extraction of clinically meaningful medical concepts from unstructured reports. Objective In this study, we aimed to determine the feasibility of using the NLP model for information extraction as an alternative approach to a time-consuming and operationally resource-intensive handcrafted rule-based tool. Therefore, we sought to develop and evaluate a deep learning-based NLP model to derive knowledge and extract information from text-based laboratory reports sourced from a provincial laboratory repository system. Methods The NLP model, a hierarchical multi-label classifier, was trained on a corpus of laboratory reports covering testing for 14 different respiratory viruses and viral subtypes. The corpus included 85 k unique laboratory reports annotated by eight Subject Matter Experts (SME). The model’s performance stability and variation were analyzed across fine-grained and coarse-grained classes. Moreover, the model’s generalizability was also evaluated internally and externally on various test sets. Results The NLP model was trained several times with random initialization on the development corpus, and the results of the top ten best-performing models are presented in this paper. Overall, the NLP model performed well on internal, out-of-time (pre-COVID-19), and external (different laboratories) test sets with micro-averaged F1 scores >94% across all classes. Higher Precision and Recall scores with less variability were observed for the internal and pre-COVID-19 test sets. As expected, the model’s performance varied across categories and virus types due to the imbalanced nature of the corpus and sample sizes per class. There were intrinsically fewer classes of viruses being detected than those tested ; therefore, the model’s performance (lowest F1-score of 57%) was noticeably lower in the “ detected ” cases. Conclusions We demonstrated that deep learning-based NLP models are promising solutions for information extraction from text-based laboratory reports. These approaches enable scalable, timely, and practical access to high-quality and encoded laboratory data if integrated into laboratory information system repositories.

Association of viral variant and vaccination status with the occurrence of symptoms compatible with post-acute sequelae after primary SARS-CoV-2 infection (preprint)

Importance: Disentangling the effects of different SARS-CoV-2 variants and of vaccination on the occurrence of post-acute sequelae of SARS-CoV-2 (PASC) is crucial to estimate and potentially reduce the future burden of PASC. Objective: To determine the association of primary SARS-CoV-2 infection on the frequency of PASC symptoms by viral variant and vaccination status. Design: Cross-sectional questionnaire and SARS-CoV-2 serology (May/June 2022) performed within a prospective healthcare worker cohort (SURPRISE study). Setting: Multicenter study in nine healthcare networks from North-Eastern Switzerland. Participants: Volunteer sample of healthcare workers (HCW) from participating institutions. Of approximately 20000 eligible participants, 3870 registered for the cohort and 2912 were included in this analysis. Exposures: SARS-CoV-2 infection documented by positive nasopharyngeal swab (>4 weeks ago), stratified by viral variant and vaccination status at time of infection, compared to absence of documented infection (no positive swab, negative serology). Main Outcome: Sum score of eighteen self-reported PASC symptoms. Results: Among 2912 participants (median age 44 years, 81.3% female), SARS-CoV-2 infection was reported by 1685 (55.9%) participants, thereof 315 (18.7%) during Wild-type, 288 (17.1%) during Alpha/Delta, and 1082 (64.2%) during Omicron circulation. Mean symptom number in previously infected participants significantly exceeded that of uninfected controls (0.39), but decreased with recency of the viral variant: 1.12 (p<0.001) for Wild-type (median time since infection 18.5 months), 0.67 (p<0.001) for Alpha/Delta (6.6 months), and 0.52 (p=0.005) for Omicron BA.1 (3.1 months) infected participants. After Omicron BA.1 infection, the mean symptom score was 0.49 (p=0.30) for those with at least 3 prior vaccinations and 0.71 (p=0.028) with 1-2 previous vaccinations compared to 0.36 for unvaccinated individuals. Adjusting for confounders, Wild-type (adjusted risk ratio [aRR] 2.81, 95% confidence interval [CI] 2.08-3.83) and Alpha/Delta infection (aRR 1.93, 95% CI 1.10-3.46) showed significant associations with the outcome, whereas Omicron BA.1 infection (aRR 1.29, 95% CI 0.69-2.43) and vaccination before infection (aRR 1.27, 95% CI 0.82-1.94) did not. Conclusions and Relevance: Previous infection with pre-Omicron variants was the strongest risk factor for reporting PASC symptoms in this HCW cohort. A definite influence of prior vaccination on the prevention of PASC after Omicron BA.1 infection was not measurable.

Association between nursing home crowding and outbreak-associated respiratory infection and death prior to the COVID-19 pandemic between 2014 and 2019 in Ontario, Canada (preprint)

Importance: Resident crowding in nursing homes is associated with larger SARS-CoV-2 outbreaks. However, this association has not been previously documented for non-SARS-CoV-2 respiratory infections. Objective: We sought to measure the association between nursing home crowding and respiratory infections in Ontario nursing homes prior to the COVID-19 pandemic. Design, Setting, and Participants: We conducted a retrospective cohort study of nursing home residents in Ontario, Canada over a five-year period prior to the COVID-19 pandemic, between September 2014 and August 2019. Exposure: Using administrative data, we estimated the crowding index equal to the mean number of residents per bedroom and bathroom (residents / [0.5*bedrooms+0.5*bathrooms]). Outcomes: The incidence of outbreak-associated infections and mortality per 100 nursing home residents per year. We also examined infection and mortality outcomes for outbreaks due to 7 specific pathogens: coronaviruses (OC43, 229E, NL63, HKU1), influenza A, influenza B, human metapneumovirus, parainfluenza virus, respiratory syncytial virus, rhinovirus/enterovirus. Results: There was one or more respiratory outbreak in 93.9% (588/626) nursing homes in Ontario. There were 4,921 outbreaks involving 64,829 cases of respiratory infection, and 1,969 deaths. Outbreaks attributable to a single identified pathogen were principally caused by influenza A (29%), rhinovirus (11.7%), influenza B (8.1%), and respiratory syncytial virus (6.1%). Among homes, 42.7% (251/588) homes had a high crowding index ([≥] 2.0). After adjustment, more crowded homes had higher outbreak-associated respiratory infection incidence (aRR 1.89; 95% 1.64-2.18) and mortality incidence (aRR 2.28; 95% 1.84- 2.84). More crowded homes had higher adjusted estimates of the incidence of infection and mortality for each of the 7 respiratory pathogens examined. Conclusions and Relevance: Residents of crowded nursing homes experienced more respiratory-outbreak infections and mortality due to influenza and other non-SARS-CoV-2 respiratory pathogens. Decreasing crowding in nursing homes is an important patient safety target beyond the COVID-19 pandemic.

Detection of COVID-19 Outbreaks in Long-Term Care Homes Using Built Environment Testing for SARS-CoV-2: A Multicentre Prospective Study (preprint)

Background Environmental surveillance of SARS-CoV-2 via wastewater has become an invaluable tool for population-level surveillance of COVID-19. Built environment sampling may provide a more spatially refined approach for surveillance of COVID-19 in congregate living settings and other high risk settings (e.g., schools, daycares). Methods We conducted a prospective study in 10 long-term care homes (LTCHs) across three cities in Ontario, Canada between September 2021 and May 2022. Floor surfaces were sampled weekly at multiple locations (range 10 to 24 swabs per building) within each building and analyzed for the presence of SARS-CoV-2 using RT-qPCR. The exposure variable was detection of SARS-CoV-2 on floors. The primary outcome was the presence of a COVID-19 outbreak in the week that floor sampling was performed. Results Over the 9-month study period, we collected 3848 swabs at 10 long-term care homes. During the study period, 19 COVID-19 outbreaks occurred with 103 cumulative weeks under outbreak. During outbreak periods, the proportion of floor swabs positive for SARS-CoV-2 was 50% (95% CI: 47-53) with a median quantification cycle of 37.3 (IQR 35.2-38.7). During non-outbreak periods the proportion of floor swabs positive was 18% (95% CI:17-20) with a median quantification cycle of 38.0 (IQR 36.4-39.1). Using the proportion of positive floor swabs for SARS-CoV-2 to predict COVID-19 outbreak status in a given week, the area under the receiver operating curve (AUROC) was 0.85 (95% CI: 0.78-0.92). Using thresholds of [≥]10%, [≥]30%, and [≥]50% of floor swabs positive for SARS-CoV-2 yielded positive predictive values for outbreak of 0.57 (0.49-0.66), 0.73 (0.63-0.81), and 0.73 (0.6-0.83) respectively and negative predictive values of 0.94 (0.87-0.97), 0.85 (0.78-0.9), and 0.75 (0.68-0.81) respectively. Among 8 LTCHs with an outbreak and swabs performed in the antecedent week, 5 had positive floor swabs exceeding 10% at least five days prior to outbreak identification. For 3 of these 5 LTCHs, positivity of floor swabs exceeded 10% more than 10 days before the outbreak being identified. Conclusions Detection of SARS-CoV-2 on floors is strongly associated with COVID-19 outbreaks in LTCHs. These data suggest a potential role for floor sampling in improving early outbreak identification.

Highly divergent white-tailed deer SARS-CoV-2 with potential deer-to-human transmission (preprint)

Wildlife reservoirs of SARS-CoV-2 can lead to viral adaptation and spillback from wildlife to humans (Oude Munnink et al., 2021). In North America, there is evidence of spillover of SARS-CoV-2 from humans to white-tailed deer (Odocoileus virginianus), but no evidence of transmission from deer to humans (Hale et al., 2021; Kotwa et al., 2022; Kuchipudi et al., 2021). Through a multidisciplinary research collaboration for SARS-CoV-2 surveillance in Canadian wildlife, we identified a new and highly divergent lineage of SARS-CoV-2. This lineage has 76 consensus mutations including 37 previously associated with non-human animal hosts, 23 of which were not previously reported in deer. There were also mutational signatures of host adaptation under neutral selection. Phylogenetic analysis revealed an epidemiologically linked human case from the same geographic region and sampling period. Together, our findings represent the first evidence of a highly divergent lineage of SARS-CoV-2 in white-tailed deer and of deer-to-human transmission.

Safety of COVID-19 vaccines in pregnancy: a Canadian National Vaccine Safety (CANVAS) Network study (preprint)

BackgroundPregnant individuals have been receiving COVID-19 vaccines following pre-authorization clinical trials in non-pregnant people. This study aimed to determine significant health events amongst pregnant females after COVID-19 vaccination, compared with unvaccinated pregnant controls and vaccinated non-pregnant individuals. MethodsStudy participants were pregnant and non-pregnant females aged 15-49 years who had received any COVID-19 vaccine, and pregnant unvaccinated controls. Participants reported significant health events occurring within seven days of vaccination. We employed multivariable logistic regression to examine significant health events associated with mRNA vaccines. FindingsOverall 226/5,597(4.0%) vaccinated pregnant females reported a significant health event after dose one of an mRNA vaccine, and 227/3,108(7.3%) after dose two, compared with 11/339(3.2%) pregnant unvaccinated females. Pregnant vaccinated females had an increased odds of a significant health event after dose two of mRNA-1273 (aOR 4.4,95%CI 2.4-8.3) compared to pregnant unvaccinated controls, but not after dose one of mRNA-1273 or any dose of BNT162b2. Pregnant females had decreased odds of a significant health event compared to non-pregnant females after both dose one (aOR 0.63,95%CI 0.55-0.72) and dose two (aOR 0.62,95%CI 0.54-0.71) of mRNA vaccination. There were no significant differences in any analyses when restricted to events which led to medical attention. InterpretationCOVID-19 mRNA vaccines have a good safety profile in pregnancy. Rates of significant health events were higher after dose two of mRNA-1273 compared with unvaccinated controls, with no difference when considering events leading to medical consultation. Rates of significant health events were lower in pregnant females than similarly aged non-pregnant individuals. FundingThis work was supported by the COVID-19 Vaccine Readiness funding from the Canadian Institutes of Health Research and the Public Health Agency of Canada CANVAS grant number CVV-450980 and by funding from the Public Health Agency of Canada, through the Vaccine Surveillance Reference Group and the COVID-19 Immunity Task Force.

Safety and Efficacy of Preventative COVID Vaccines: The StopCoV Study (preprint)

Background: To partially immunize more persons against COVID-19 during a time of limited vaccine availability, Canadian public health officials recommended extending the vaccine dose interval and brand mixing. Impact on the antibody response among the older ambulatory population was unclear. Methods: Decentralized prospective cohort study with self-report of adverse events and collection of dried blood spots. Data is presented for 1193 (93%) of the 911 older (aged >70 years) and 375 younger (30-50 years) recruits. Findings: Local and systemic reactivity rates were high but short-lived, particularly in the younger cohort and with mRNA-1273 vaccine. After a single COVID-19 vaccine, 84% younger but only 46% older participants had positive IgG antibodies to both spike protein and receptor binding domain (RBD) antigens, increasing to 100/98% with the second dose respectively. In multivariable linear regression model, lower normalized IgG RBD antibody ratios two weeks after the second dose were statistically associated with older age, male gender, cancer diagnosis, lower body weight, BNT162b2 relative to mRNA-1273 and longer dose intervals. Antibody ratios in both cohorts declined 12 weeks post second vaccine dose. Interpretation: We report success of a decentralized serology study. Antibody responses were higher in the younger than older cohort and were greater for those with at least one mRNA-1273 dose. The immunity threshold is unknown but correlations between binding and neutralizing antibodies are strongly positive. Trends with time and at breakthrough infection will inform vaccine booster strategies. Funding: Supported by the Public Health Agency of Canada and the University Health Network Foundation.

Longitudinal Assessment of SARS-CoV-2 Specific T Cell Cytokine-Producing Responses for 1 Year Reveals Persistence of Multi-Cytokine Proliferative Responses, with Greater Immunity Associated with Disease Severity (preprint)

Cellular-mediated immunity is critical for long-term protection against most viral infections, including coronaviruses. We studied 23 SARS-CoV-2-infected survivors over a one year post symptom onset (PSO) interval by ex vivo cytokine ELISpot assay. All subjects demonstrated SARS-CoV-2-specific IFN-{gamma}, IL-2, and Granzyme B (GzmB) T cell responses at presentation, with greater frequencies in severe disease. Cytokines, mainly produced by CD4+ T cells, targeted all structural proteins (Nucleocapsid, Membrane, Spike) except Envelope, with GzmB > IL-2 > IFN-{gamma}. Mathematical modeling predicted that: 1) cytokine responses peaked at 6 days for IFN-{gamma}, 36 days for IL-2, and 7 days for GzmB, 2) severe illness was associated with reduced IFN-{gamma} and GzmB, but increased IL-2 production rates, 3) males displayed greater production of IFN-{gamma}, whereas females produced more GzmB. Ex vivo responses declined over time with persistence of IL-2 in 86% and of IFN-{gamma} and GzmB in 70% of subjects at a median of 336 days PSO. The average half-life of SARS-CoV-2-specific cytokine-producing cells was modelled to be 139 days (~4.6 months). Potent T cell proliferative responses persisted throughout observation, were CD4 dominant, and were capable of producing all 3 cytokines. Several immunodominant CD4 and CD8 epitopes identified in this study were shared by seasonal coronaviruses or SARS-CoV-1 in the Nucleocapsid and Membrane regions. Both SARS-CoV-2-specific CD4+ and CD8+ T cell clones were able to kill target cells, though CD8 tended to be more potent.

Symptoms compatible with long-COVID in healthcare workers with and without SARS-CoV-2 infection - results of a prospective multicenter cohort (preprint)

Background: The burden of long-term symptoms (i.e. long-COVID) in patients after mild COVID-19 is debated. Within a cohort of healthcare workers (HCW), frequency and risk factors for symptoms compatible with long-COVID are assessed. Methods: Participants answered baseline (August/September 2020) and weekly questionnaires on SARS-CoV-2 nasopharyngeal swab (NPS) results and acute disease symptoms. In January 2021, SARS-CoV-2 serology was performed; in March, symptoms compatible with long-COVID (including psychometric scores) were asked and compared between HCW with positive NPS, seropositive HCW without positive NPS (presumable a-/pauci-symptomatic infections), and negative controls. Also, the effect of time since diagnosis and quantitative anti-S was evaluated. Poisson regression was used to identify risk factors for symptom occurrence. Results: Of 3334 HCW (median 41 years; 80% female), 556 (17%) had a positive NPS and 228 (7%) were only seropositive. HCW with positive NPS more frequently reported [≥]1 symptom compared to controls (73%vs.52%, p<0.001); seropositive HCW without positive NPS did not score higher than controls (58%vs.52%, p=0.13), although impaired taste/olfaction (16%vs.6%, p<0.001) and hair loss (17%vs.10%, p=0.004) were more common. Exhaustion/burnout was reported by 24% of negative controls. Many symptoms remained elevated in those diagnosed >6 months ago; anti-S titers correlated with high symptom scores. Acute viral symptoms in weekly questionnaires best predicted long-COVID symptoms. Physical activity at baseline was negatively associated with neurocognitive impairment and fatigue scores. Conclusions: Seropositive HCW without positive NPS are only mildly affected by long-COVID. Exhaustion/burnout is common, even in non-infected HCW. Physical activity might be protective against neurocognitive impairment/fatigue symptoms after COVID-19.

Intramuscular SARS-CoV-2 vaccines elicit varying degrees of plasma and salivary antibody responses as compared to natural infection (preprint)

Vaccination induced antibody and T-cell immune responses are important for systemic protection from COVID-19. Because SARS-CoV-2 infects and is transmitted by oral-pharyngeal mucosa, we wished to test mucosal antibodies elicited by natural infection or intramuscular vaccine injection. In a non-randomized observational study, we measured antibodies against the SARS-CoV-2 RBD in plasma and saliva from convalescent or vaccinated individuals and tested their neutralizing potential using a replication competent rVSV-eGFP-SARS-CoV-2. We found IgG and IgA anti-RBD antibodies as well as neutralizing activity in convalescent plasma and saliva. Two doses of mRNA vaccination (BNT162b2 or mRNA-1273) induced high levels of IgG anti-RBD in saliva, a subset of whom also had IgA, and significant neutralizing activity. We detected anti-RBD IgG and IgA with significant neutralizing potential in the plasma of single dose Ad26.COV2.S vaccinated individuals, and we detected slight amounts of anti-RBD antibodies in matched saliva. The role of salivary antibodies in protection against SARS-CoV-2 infection is unknown and merits further investigation. This study was not designed to, nor did it study the full kinetics of the antibody response or protection from infection, nor did it address variants of SARS-CoV-2.

A mucosal antibody response is induced by intra-muscular SARS-CoV-2 mRNA vaccination (preprint)

The first line of defense against SARS-CoV-2 is the upper respiratory tract, yet we know little about the amount, type, and kinetics of mucosal anti-Spike antibodies (Ab) in response to intramuscular (i.m.) COVID-19 vaccination. We analyzed salivary Ab against SARS-CoV-2 Spike following mRNA/mRNA and adenovirus (Ad)/mRNA regimes. While anti-Spike/RBD IgG was detected in the saliva and correlated with the systemic response, anti-Spike/RBD IgA associated with the secretory component (sIgA) was also detected, and did not necessarily correlate with serum Ab. Only modest levels of neutralizing capacity were observed in saliva at 2 weeks post-dose 2, and by 6 months, anti-Spike/RBD IgG were greatly diminished. In contrast, low levels of anti-Spike sIgA persisted up to 6 months after dose 2. Our results show that SARS-CoV-2 vaccination induces an IgG response in the saliva that decays over time and an sIgA response that does not necessarily correlate with systemic immunity. One-Sentence SummaryOur study delves into how intra-muscular mRNA/mRNA or mRNA/Ad COVID-19 vaccination regimes confer immunity in the oral cavity with important implications for understanding protection against breakthrough infections in healthy vaccinated people.

Convalescent plasma for hospitalized patients with COVID-19 and the effect of plasma antibodies: a randomized controlled, open-label trial (preprint)

The efficacy of convalescent plasma for COVID-19 is unclear. While most randomized controlled trials have shown negative results, uncontrolled studies have suggested that the antibody content may influence patient outcomes. We conducted an open-label, randomized controlled trial of convalescent plasma for adults with COVID-19 receiving oxygen within 12 days of respiratory symptom onset. Patients were allocated 2:1 to 500 mL of convalescent plasma or standard of care. The composite primary outcome was intubation or death by 30 days. The effect of convalescent plasma antibodies on the primary outcome was assessed by logistic regression. The trial was terminated at 78% of planned enrollment after meeting stopping criteria for futility. 940 patients were randomized and 921 patients were included in the intent-to-treat analysis. Intubation or death occurred in 199/614 (32.4%) in the convalescent plasma arm and 86/307 (28.0%) in the standard of care arm; relative risk (RR) 1.16 (95% confidence interval (CI) 0.94-1.43; p=0.18). Patients in the convalescent plasma arm had more serious adverse events (33.4% vs. 26.4%; RR=1.27, 95% CI 1.02-1.57, p=0.034). The antibody content significantly modulated the therapeutic effect of convalescent plasma. In multivariate analysis, each standard log increase in neutralization or antibody-dependent cellular cytotoxicity independently reduced the potential harmful effect of plasma (OR=0.74; 0.57-0.95 and OR=0.66; 0.50-0.87, respectively), while IgG against the full transmembrane Spike protein increased it (OR=1.53, 95% CI 1.14-2.05). Convalescent plasma did not reduce the risk of intubation or death at 30 days among hospitalized patients with COVID-19. Transfusion of convalescent plasma with unfavourable antibody profiles may be associated with worse clinical outcomes compared to standard care.

Impact of baseline SARS-CoV-2 antibody status on syndromic surveillance and the risk of subsequent Covid-19 -- a prospective multicentre cohort study (preprint)

Objectives In a prospective healthcare worker (HCW) cohort, we assessed the risk of SARS-CoV-2 infection according to baseline serostatus. Methods Baseline serologies were performed among HCW from 23 Swiss healthcare institutions between June and September 2020, before the second COVID-19 wave. Participants answered weekly electronic questionnaires covering information about nasopharyngeal swabs (PCR/rapid antigen tests) and symptoms compatible with Coronavirus Disease 2019 (COVID-19). Screening of symptomatic staff by nasopharyngeal swabs was routinely performed in participating facilities. We compared numbers of positive nasopharyngeal tests and occurrence of COVID-19 symptoms between HCW with and without anti-nucleocapsid antibodies. Results A total of 4'818 HCW participated, whereof 144 (3%) were seropositive at baseline. We analysed 107'820 questionnaires with a median follow-up of 7.9 months. Median number of answered questionnaires was similar (24 vs. 23 per person, P=0.83) between those with and without positive baseline serology. Among 2'713 HCW with [≥]1 SARS-CoV-2 test during follow-up, 3/67 (4.5%) seropositive individuals reported a positive result (one of whom asymptomatic), compared to 547/2646 (20.7%) seronegative participants, 12 of whom asymptomatic (risk ratio [RR] 0.22; 95% confidence interval [CI] 0.07 to 0.66). Seropositive HCWs less frequently reported impaired olfaction/taste (6/144, 4.2% vs. 588/4674, 12.6%, RR 0.33, 95%-CI: 0.15-0.73), chills (19/144, 13.2% vs. 1040/4674, 22.3%, RR 0.59, 95%-CI: 0.39-0.90), and limb/muscle pain (28/144, 19.4% vs. 1335/4674, 28.6%, RR 0.68 95%-CI: 0.49-0.95). Impaired olfaction/taste and limb/muscle pain also discriminated best between positive and negative SARS-CoV-2 results. Conclusions Having SARS-CoV-2 anti-nucleocapsid antibodies provides almost 80% protection against SARS-CoV-2 re-infection for a period of at least eight months.

Use of respirator vs. surgical masks in healthcare personnel and its impact on SARS-CoV-2 acquisition – a prospective multicentre cohort study (preprint)

ABSTRACT Background There is insufficient evidence regarding the role of respirators in the prevention of SARS-CoV-2 infection. We analysed the impact of filtering facepiece class 2 (FFP2) vs . surgical masks on the risk of SARS-CoV-2 acquisition among Swiss healthcare workers (HCW). Methods Our prospective multicentre cohort enrolled patient-facing HCWs from June to August 2020. Participants were asked about COVID-19 risk exposures/behaviours, including preferred mask type when caring for COVID-19 patients outside of aerosol-generating procedures (AGP). For those performing AGPs, we asked whether they used FFP2 irrespective of the patient’s COVID-19 status (i.e. universal use). The impact of FFP2 on i) self-reported SARS-CoV-2-positive nasopharyngeal PCR/rapid antigen tests captured during weekly surveys, and ii) SARS-CoV-2 seroconversion between baseline and January/February 2021 was assessed. Results We enrolled 3’259 participants from nine healthcare institutions, whereof 716 (22%) preferentially used FFP2 respirators. Among these, 81/716 (11%) reported a SARS-CoV-2-positive swab, compared to 352/2543 (14%) surgical mask users (median follow-up 242 days); seroconversion was documented in 85/656 (13%) FFP2 and 426/2255 (19%) surgical mask users. Adjusted for baseline characteristics, COVID-19 exposure, and risk behaviour, FFP2 use was non-significantly associated with a decreased risk for SARS-CoV-2-positive swab (adjusted hazard ratio [aHR] 0·8, 95% CI 0·6-1·0, p=0·052) and seroconversion (adjusted odds ratio [aOR] 0·7, 95% CI 0·5-1·0, p=0·053); household exposure was the strongest risk factor (aHR for positive swab 10·1, p<0·001; aOR for seroconversion 5·0, p<0·001). In subgroup analysis, FFP2 use was clearly protective among those with frequent (>20 patients) COVID-19 exposure (aHR 0·7, p<0·001; aOR 0·6, p=0·035). Universal FFP2 use during AGPs showed no protective effect (aHR 1·1, p=0·7; aOR 0·9, p=0·53). Conclusion Respirators compared to surgical masks may convey additional protection from SARS-CoV-2 for HCW with frequent exposure to COVID-19 patients. Funding Swiss National Sciences Foundation, Federal Office of Public Health, Cantonal Health Department St.Gallen

Dried blood spot specimens for SARS-CoV-2 antibody testing: A multi-site, multi-assay comparison (preprint)

The true severity of infection due to COVID-19 is under-represented because it is based on only those who are tested. Although nucleic acid amplifications tests (NAAT) are the gold standard for COVID-19 diagnostic testing, serological assays provide better population-level SARS-CoV-2 prevalence estimates. Implementing large sero-surveys present several logistical challenges within Canada due its unique geography including rural and remote communities. Dried blood spot (DBS) sampling is a practical solution but comparative performance data on SARS-CoV-2 serological tests using DBS is currently lacking. Here we present test performance data from a well-characterized SARS-CoV-2 DBS panel sent to laboratories across Canada representing 10 commercial and 2 in-house developed tests for SARS-CoV-2 antibodies. Three commercial assays identified all positive and negative DBS correctly corresponding to a sensitivity, specificity, positive predictive value, and negative predictive value of 100% (95% CI = 72.2, 100). Two in-house assays also performed equally well. In contrast, several commercial assays could not achieve a sensitivity greater than 40% or a negative predictive value greater than 60%. Our findings represent the foundation for future validation studies on DBS specimens that will play a central role in strengthening Canada’s public health policy in response to COVID-19.

Convalescent plasma for adults with acute COVID-19 respiratory illness (CONCOR-1): Study protocol for an international, multicenter, randomized, open-label trial (preprint)

Background: Convalescent plasma has been used for numerous viral diseases including influenza, severe acute respiratory syndrome, Middle East respiratory syndrome and Ebola virus; however, evidence to support its use is weak. SARS-CoV-2 is a novel coronavirus responsible for the 2019 global pandemic of COVID-19 community acquired pneumonia. We have undertaken a randomized controlled trial to assess the efficacy and safety of COVID-19 convalescent plasma (CCP) in patients with SARS-CoV-2 infection.Methods: CONCOR-1 is an open-label, multicenter, randomized trial. Inclusion criteria include: patients >16 years; admitted to hospital with COVID-19 infection; receiving supplemental oxygen for respiratory complications of COVID-19; and, availability of blood group compatible CCP. Exclusion criteria are: onset of respiratory symptoms more than 12 days prior to randomization; intubated or planned for intubation; and previous severe reactions to plasma. Consenting patients will be randomized 2:1 to receive either approximately 500 mL of CCP or standard of care. CCP will be collected from donors who have recovered from COVID-19 and who have detectable anti-SARS-CoV-2 antibodies quantified serologically. The primary outcome is intubation or death at Day 30. Secondary outcomes include ventilator free days, length of stay in intensive care or hospital, transfusion reactions, serious adverse events, and reduction in SARS-CoV-2 viral load.  Exploratory analyses include patients who received CCP containing high titre antibodies. A sample size of 1200 patients gives 80% power to detect a 25% relative risk reduction assuming a 30% baseline risk of intubation or death at 30 days (two-sided test; α =0.05). An interim analysis and sample size re-estimation will be done by an unblinded independent biostatistician after primary outcome data are available for 50% of the target recruitment (n= 600). Discussion: This trial will determine whether CCP will reduce intubation or death non-intubated adults with COVID-19. The trial will also provide information on the role of and thresholds for SARS-CoV-2 antibody titers and neutralization assays for donor qualification.Trial registration: Clinicaltrials.gov NCT04348656; registered 16 April 2020; https://clinicaltrials.gov/ct2/show/NCT04348656?term=NCT04348656&draw=2&rank=1

Ultrasensitive assay for saliva-based SARS-CoV-2 antigen detection. (preprint)

Widespread SARS-CoV-2 testing is highly valuable for identifying asymptomatic/pre-symptomatic individuals to slow community disease transmission. However, there remains a technological gap for highly reliable, easy, and quick SARS-CoV-2 diagnostic tests that are suitable for frequent mass testing. Compared to the conventional nasopharyngeal (NP) swab-based tests, saliva-based methods are attractive due to easier and safer sampling protocols. Despite its merits in rapid turn-around-time and high throughput compared to traditional PCR-based technologies, the widespread use of saliva-based SARS-CoV-2 rapid antigen tests is hindered by limited analytical sensitivity of current methods. Here, we report the first ultrasensitive, saliva-based SARS-CoV-2 antigen assay with an analytical sensitivity of < 0.32 pg/ml, corresponding to 4 viral RNA copies/{micro}l, which is comparable to that of PCR-based tests. Using the novel electrochemiluminescence (ECL)-based S-PLEX immunoassay, we measured the SARS-CoV-2 nucleocapsid (N) antigen concentration in 105 saliva samples obtained from non-COVID-19 and COVID-19 patients. Our assay displayed absolute specificity and high sensitivity (90.2%), where it correctly identified samples with viral loads up to 35 CT cycles by saliva-based PCR. Paired NP swab-based PCR results were also obtained for 86 cases for comparison. Our assay showed high concordance with saliva-based and NP swab-based PCR in samples with negative (< 0.32 pg/ml) and strongly positive (> 2 pg/ml) N antigen concentrations. Our study unveiled the ultrasensitivity and specificity of the saliva-based S-PLEX assay, demonstrating its clinical value as a high throughput, complementary alternative to PCR-based techniques. The novel technique is especially valuable in cases where compliance to frequent swabbing may be problematic (e.g. schools, nursing homes, etc.).