Distinct phenotype of SARS-CoV-2 Omicron BA.1 in human primary cells but no increased host range in cell lines of putative mammalian reservoir species (preprint)

SARS-CoV-2's genetic plasticity has led to several variants of concern (VOCs). Here we studied replicative capacity for seven SARS-CoV-2 isolates (B.1, Alpha, Beta, Gamma, Delta, Zeta, and Omicron BA.1) in primary reconstituted airway epithelia (HAE) and lung-derived cell lines. Furthermore, to investigate the host range of Delta and Omicron compared to ancestral SARS-CoV-2, we assessed replication in 17 cell lines from 11 non-primate mammalian species, including bats, rodents, insectivores and carnivores. Only Omicron's phenotype differed in vitro, with rapid but short replication and efficient production of infectious virus in nasal HAEs, in contrast to other VOCs, but not in lung cell lines. No increased infection efficiency for other species was observed, but Delta and Omicron infection efficiency was increased in A549 cells. Notably replication in A549 and Calu3 cells was lower than in nasal HAE. Our results suggest better adaptation of VOCs towards humans, without an extended host range.

SARS-CoV-2 infections in nasal epithelial cells from smokers versus non-smokers (preprint)

Whether smoking exacerbates Coronavirus disease 2019 is still debated. Ex-vivo Infection of reconstituted epithelial tissues from smoker versus non-smoker donors suggested comparable susceptibility to SARS-CoV-2 in epithelia from both groups.

Diagnostic accuracy of two commercial SARS-CoV-2 Antigen-detecting rapid tests at the point of care in community-based testing centers (preprint)

BackgroundAntigen-detecting rapid diagnostic tests for SARS-CoV-2 offer new opportunities for the quick and laboratory-independent identification of infected individuals for control of the SARS-CoV-2 pandemic. MethodsWe performed a prospective, single-center, point of care validation of two antigen-detecting rapid diagnostic tests (Ag-RDT) in comparison to RT-PCR on nasopharyngeal swabs. FindingsBetween October 9th and 23rd, 2020, 1064 participants were enrolled. The PanbioCovid-19 Ag Rapid Test device (Abbott) was validated in 535 participants, with 106 positive Ag-RDT results out of 124 positive RT-PCR individuals, yielding a sensitivity of 85.5% (95% CI: 78.0-91.2). Specificity was 100.0% (95% CI: 99.1-100) in 411 RT-PCR negative individuals. The Standard Q Ag-RDT (SD Biosensor, Roche) was validated in 529 participants, with 170 positive Ag-RDT results out of 191 positive RT-PCR individuals, yielding a sensitivity of 89.0% (95%CI: 83.7-93.1). One false positive result was obtained in 338 RT-PCR negative individuals, yielding a specificity of 99.7% (95%CI: 98.4-100). For individuals presenting with fever 1-5 days post symptom onset, combined Ag-RDT sensitivity was above 95%. InterpretationWe provide an independent validation of two widely available commercial Ag-RDTs, both meeting WHO criteria of [≥]80% sensitivity and [≥]97% specificity. Although less sensitive than RT-PCR, these assays could be beneficial due to their rapid results, ease of use, and independence from existing laboratory structures. Testing criteria focusing on patients with typical symptoms in their early symptomatic period onset could further increase diagnostic value. FundingFoundation of Innovative Diagnostics (FIND), Fondation privee des HUG, Pictet Charitable Foundation.

Validation and clinical evaluation of a SARS-CoV-2 Surrogate Virus Neutralization Test (sVNT) (preprint)

To understand SARS-CoV-2 immunity after natural infection or vaccination, functional assays such as virus neutralizing assays are needed. So far, assays to determine SARS-CoV-2 neutralizing antibodies rely on cell-culture based infection assays either using wild type SARS-CoV-2 or pseudotyped viruses. Such assays are labour-intensive, require appropriate biosafety facilities and are difficult to standardize. Recently, a new surrogate virus neutralisation assay (sVNT) was described that uses the principle of an ELISA to measure the neutralization capacity of anti-SARS-CoV-2 antibodies directed against the receptor binding domain. Here, we performed an independent evaluation of the robustness, specificity and sensitivity on an extensive panel of sera from 269 PCR-confirmed COVID-19 cases and 259 unmatched samples collected before 2020 and compared it to cell-based neutralization assays. We found a high specificity of 99.2 (95%CI: 96.9-99.9) and overall sensitivity of 80.3 (95%CI: 74.9-84.8) for the sVNT. Clinical sensitivity increased between early (<14 days post symptom onset or post diagnosis, dpos/dpd) and late sera (>14 dpos/dpd) from 75.0 (64.7-83.2) to 83.1 (76.5-88.1). Also, higher severity was associated with an increase in clinical sensitivity. Upon comparison with cell-based neutralisation assays we determined an analytical sensitivity of 74.3 (56.4-86.9) and 98.2 (89.4-99.9) for titres [≥]10 to <40 and [≥]40 to <160, respectively. Only samples with a titre [≥]160 were always positive in the sVNT. In conclusion, the sVNT can be used as an additional assay to determine the immune status of COVID-19 infected of vaccinated individuals but its value needs to be assessed for the specific context of use.

Daily viral kinetics and innate and adaptive immune responses assessment in COVID-19: a case series (preprint)

BackgroundViral shedding patterns and its correlation with the immune responses of mildly symptomatic COVID-19 patients are still poorly characterized. MethodsWe enrolled the first five COVID-19 patients quarantined in our institution; none received immunomodulatory treatment. We monitored shedding of viral RNA and infectious virus by RT-PCR and cell culture from the upper respiratory tract, and characterized the kinetics of systemic innate and adaptive immune responses. ResultsDespite mild clinical disease, high viral loads and shedding of infectious virus were observed from the respiratory tract, with isolation of infectious virus and prolonged positivity by PCR up to day 7 and 19 post onset of symptoms, respectively. Robust innate responses characterized by an increase in activated CD14+CD16+ monocytes and cytokine responses were observed as early as 2 days after symptoms onset. Cellular and humoral SARS-CoV-2 specific adaptive responses were detectable in all patients. ConclusionInfectious virus shedding was limited to the first week of symptom onset in mild cases. A strong innate response, characterized by the mobilization of activated monocytes during the first days of infection, as well as SARS-CoV-2 specific antibodies were detectable, even in patients with mild disease. SummaryWe describe viral and immune profiles of the first five SARS-CoV-2 patients in our institution, showing high viral loads and infectious viral shedding in early acute disease. Mild patients mount an innate response sufficient for viral control and specific immunity.

Validation of a commercially available SARS-CoV-2 serological Immunoassay (preprint)

Aims: To validate the diagnostic accuracy of a Euroimmun SARS-CoV-2 IgG and IgA immunoassay for COVID-19 disease. Methods: In this unmatched (1:1) case-control validation study, we used sera of 181 laboratory-confirmed SARS-CoV-2 cases and 176 negative controls collected before the emergence of SARS-CoV-2. Diagnostic accuracy of the immunoassay was assessed against a whole spike protein-based recombinant immunofluorescence assay (rIFA) by receiver operating characteristic (ROC) analyses. Discrepant cases between ELISA and rIFA were further tested by pseudo-neutralization assay. Results: COVID-19 patients were more likely to be male and older than controls, and 50.3% of them were hospitalized. ROC curve analyses indicated that IgG and IgA had a high diagnostic accuracy with AUCs of 0.992 (95% Confidence Interval [95%CI]: 0.986-0.996) and 0.977 (95%CI: 0.963-0.990), respectively. IgG assays outperformed IgA assays (p=0.008). Considering optimized cut-offs taking the 15% inter-assay imprecision assessed into account, an IgG ratio cut-off > 1.5 displayed a 100% specificity (95%CI: 98-100) and a 100% positive predictive value (95%CI: 97-100). A 0.5 cut-off displayed a 97% sensitivity (95%CI: 93-99) and a 97% negative predictive value (95%CI: 93-99). Adopting these thresholds, rather than those of the manufacturer, improved assay performance, leaving 12% of IgG ratios ranging between 0.5-1.5 as indeterminate. Conclusions: The Euroimmun assay displays a nearly optimal diagnostic accuracy using IgG against SARS-CoV-2 in a samples of patients, without any obvious gains from considering IgA serology. The optimized cut-offs are fit for rule-in and rule-out purposes, allowing determination of whether individuals have been exposed to SARS-CoV-2 or not in our study population. They should however not be considered as a surrogate of protection at this stage.

Shedding of infectious SARS-CoV-2 in symptomatic neonates, children and adolescents (preprint)

Children are underrepresented in COVID-19 case numbers, with most pediatric cases exhibiting limited severity, and do not seem to be major drivers of transmission, unlike for other respiratory viruses. That said, SARS-CoV-2 infects children across all age groups, and despite the high proportion of mild or asymptomatic infections, it would be naive not to consider them as transmitters. To address this point we used cell culture to systematically assess the presence of cultivable SARS-CoV-2 in the upper respiratory tract in a cohort of our institution first 23 symptomatic neonates, children and teenagers with COVID-19 diagnosed by RT-PCR (See Appendix). Median age was 12.0 years (interquartile range [IQR 3.8-14.5], range 7 days-15.9 yrs). Most patients had an upper respiratory tract infection (n=13), followed by fever without source and pneumonia (each, n=2). Samples were collected at a median of 2 days (IQR 1-3) after symptom onset. Median viral load (VL) at time of diagnosis was 3.0x106 copies/ml (mean 4,4x108, IQR 6.9x103-4.4x108) from a nasopharyngeal swab (NPS). SARS-CoV-2 virus isolation was successful in 12/23 (52%) children after inoculating VeroE6 cells with a NPS specimen. SARS-CoV-2 isolation was determined by the presence of a typical cytopathic effect (CPE) and increased viral RNA in the supernatant. SARS-CoV-2 replication in all positive isolates (12/12) was confirmed by a second passage using new VeroE6 cells. Virus isolation was successful from NPS from all age groups, with a median initial VL of 1.7x108 copies/ml (mean 7.9x108, IQR 4.7x106-1.0x109) (Figure 1). The youngest patient that SARS-CoV-2 was isolated from was a 7-day old neonate. No correlation between disease presentation and success of virus isolation was observed. Our data show that initial VLs at diagnosis in symptomatic children is comparable to those in adults, and that symptomatic children of all ages shed infectious virus in early acute illness. Infectious virus isolation success was largely comparable to that of adults, although two specimens yielded an isolate at a lower VL (1.2x104 and 1.4x105 copies/ml) than what was observed in adults. SARS-CoV-2 shedding patterns of culture competent virus in symptomatic children resemble those observed in adults. Therefore, transmission of SARS-CoV-2 from children is plausible. Considering the relatively low frequency of infected children at this time, biological or other unknown factors could reduce transmission in this population. Both large serological investigations and systematic surveillance of acute respiratory diseases are needed to understand the role of children in this new pandemic.