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      Decreased Sensitivity of Rapid Antigen Test Is Associated with a Lower Viral Load of Omicron than Delta SARS-CoV-2 Variant


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          Large-scale screening for SARS-CoV-2 infection is an important tool for epidemic prevention and control. The appearance of new variants associated with specific mutations can call into question the effectiveness of rapid diagnostic tests (RDTs) deployed massively at national and international levels. We compared the clinical and virological characteristics of individuals infected by Delta or Omicron variants to assess which factors were associated with a reduced performance of RDT. A commercially available RDT as well as the evaluation of the viral load (VL) and the detection of replicate intermediates (RIs) were carried out retrospectively on positive SARS-CoV-2 nasopharyngeal specimens from health care workers of the Pitié-Salpêtrière Hospital infected by the Delta or Omicron variant between July 2021 and January 2022. Of the 205 samples analyzed (104 from individuals infected with Delta and 101 with Omicron), 176 were analyzed by RDT and 200 by RT-PCR for VL and RIs. The sensitivity of the TDR for Omicron was significantly lower than that observed for Delta (53.8% versus 74.7%, respectively, P < 0.01). Moreover, the Delta VL was significantly higher than that measured for Omicron (median Ct 21.2 versus 24.1, respectively, P < 0.01) and associated with the positivity of the RDT in multivariate analysis. We demonstrate a lower RDT sensitivity associated with a lower VL at the time of diagnosis on Omicron-infected individuals in comparison to those infected with the Delta variant. This RDT lower sensitivity should be taken into account in the large-scale screening strategy and in particular in case of strong suspicion of infection where testing should be repeated.

          IMPORTANCE Previous reports have shown a variability in the diagnostic performance of RDTs. In the era of SARS-CoV-2 variants and the use of RDT, mutation associated with these variants could affect the test performance. We evaluate the sensitivity of the RDT Panbio COVID-19 Ag (Abbott) with two variants of concern (VOC), the Delta and Omicron variants. In order to investigate whether clinical characteristics or virological characteristics can affect this sensitivity, we collected clinical information and performed a specific RT-PCR that detected the RIs as a marker of the viral replication and viral cycle stage. Our results showed that Omicron was less detected than the Delta variant. A lower viral load of Omicron variant in comparison to Delta variant explained this decreased sensitivity, even if they are at the same stage of the disease and the viral cycle and should be taken into account with the use of RDT as diagnostic tool.

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          Symptom prevalence, duration, and risk of hospital admission in individuals infected with SARS-CoV-2 during periods of omicron and delta variant dominance: a prospective observational study from the ZOE COVID Study

          Background The SARS-CoV-2 variant of concern, omicron, appears to be less severe than delta. We aim to quantify the differences in symptom prevalence, risk of hospital admission, and symptom duration among the vaccinated population. Methods In this prospective longitudinal observational study, we collected data from participants who were self-reporting test results and symptoms in the ZOE COVID app (previously known as the COVID Symptoms Study App). Eligible participants were aged 16–99 years, based in the UK, with a body-mass index between 15 and 55 kg/m 2 , had received at least two doses of any SARS-CoV-2 vaccine, were symptomatic, and logged a positive symptomatic PCR or lateral flow result for SARS-CoV-2 during the study period. The primary outcome was the likelihood of developing a given symptom (of the 32 monitored in the app) or hospital admission within 7 days before or after the positive test in participants infected during omicron prevalence compared with those infected during delta prevalence. Findings Between June 1, 2021, and Jan 17, 2022, we identified 63 002 participants who tested positive for SARS-CoV-2 and reported symptoms in the ZOE app. These patients were matched 1:1 for age, sex, and vaccination dose, across two periods (June 1 to Nov 27, 2021, delta prevalent at >70%; n=4990, and Dec 20, 2021, to Jan 17, 2022, omicron prevalent at >70%; n=4990). Loss of smell was less common in participants infected during omicron prevalence than during delta prevalence (16·7% vs 52·7%, odds ratio [OR] 0·17; 95% CI 0·16–0·19, p<0·001). Sore throat was more common during omicron prevalence than during delta prevalence (70·5% vs 60·8%, 1·55; 1·43–1·69, p<0·001). There was a lower rate of hospital admission during omicron prevalence than during delta prevalence (1·9% vs 2·6%, OR 0·75; 95% CI 0·57–0·98, p=0·03). Interpretation The prevalence of symptoms that characterise an omicron infection differs from those of the delta SARS-CoV-2 variant, apparently with less involvement of the lower respiratory tract and reduced probability of hospital admission. Our data indicate a shorter period of illness and potentially of infectiousness which should impact work–health policies and public health advice. Funding Wellcome Trust, ZOE, National Institute for Health Research, Chronic Disease Research Foundation, National Institutes of Health, and Medical Research Council
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            Infectious viral load in unvaccinated and vaccinated individuals infected with ancestral, Delta or Omicron SARS-CoV-2

            Infectious viral load (VL) expelled as droplets and aerosols by infected individuals partly determines transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). RNA VL measured by qRT-PCR is only a weak proxy for infectiousness. Studies on the kinetics of infectious VL are important to understand the mechanisms behind the different transmissibility of SARS-CoV-2 variants and the effect of vaccination on transmission, which allows guidance of public health measures. In this study, we quantified infectious VL in individuals infected with SARS-CoV-2 during the first five symptomatic days by in vitro culturability assay in unvaccinated or vaccinated individuals infected with pre-variant of concern (pre-VOC) SARS-CoV-2, Delta or Omicron BA.1. Unvaccinated individuals infected with pre-VOC SARS-CoV-2 had lower infectious VL than Delta-infected unvaccinated individuals. Full vaccination (defined as >2 weeks after receipt of the second dose during the primary vaccination series) significantly reduced infectious VL for Delta breakthrough cases compared to unvaccinated individuals. For Omicron BA.1 breakthrough cases, reduced infectious VL was observed only in boosted but not in fully vaccinated individuals compared to unvaccinated individuals. In addition, infectious VL was lower in fully vaccinated Omicron BA.1-infected individuals compared to fully vaccinated Delta-infected individuals, suggesting that mechanisms other than increased infectious VL contribute to the high infectiousness of SARS-CoV-2 Omicron BA.1. Our findings indicate that vaccines may lower transmission risk and, therefore, have a public health benefit beyond the individual protection from severe disease.
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              Comparison of Patients Infected With Delta Versus Omicron COVID-19 Variants Presenting to Paris Emergency Departments

              At the end of 2021, infections with the B.1.1.529 SARS-CoV-2 variant (Omicron) superseded those with the B.1.617.2 variant (Delta). This study compares baseline characteristics and in-hospital outcomes of patients who presented to 13 emergency departments in Paris from 29 November 2021 to 10 January 2022.

                Author and article information

                Role: Editor
                Microbiol Spectr
                Microbiol Spectr
                Microbiology Spectrum
                American Society for Microbiology (1752 N St., N.W., Washington, DC )
                20 September 2022
                Sep-Oct 2022
                20 September 2022
                : 10
                : 5
                : e01922-22
                [a ] INSERM, Institut Pierre Louis d’Epidémiologie et de Santé Publique, Assistance Publique-Hôpitaux de Paris (AP-HP), Hôpital Pitié-Salpêtrière, Service, Department of Virology, Sorbonne Université, Paris, France
                [b ] INSERM, Institut Pierre Louis d'Epidémiologie et de Santé Publique, Sorbonne Université, Paris, France
                [c ] Hôpital Pitié-Salpêtrière, Service de Santé au Travail, Assistance Publique-Hôpitaux de Paris, Sorbonne Université, Paris, France
                Quest Diagnostics
                Author notes

                The authors declare no conflict of interest.

                Author information
                01922-22 spectrum.01922-22
                Copyright © 2022 Cocherie et al.

                This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.

                : 23 May 2022
                : 26 August 2022
                Page count
                supplementary-material: 0, Figures: 0, Tables: 2, Equations: 0, References: 13, Pages: 5, Words: 3242
                open-peer-review, Open Peer Review
                applied-and-industrial-microbiology, Applied and Industrial Microbiology
                Custom metadata
                September/October 2022

                covid-19,sars-cov-2,antigen,diagnostics,viral load
                covid-19, sars-cov-2, antigen, diagnostics, viral load


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