SARS-CoV-2 viral load and shedding kinetics

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Abstract

SARS-CoV-2 viral load and detection of infectious virus in the respiratory tract are the two key parameters for estimating infectiousness. As shedding of infectious virus is required for onward transmission, understanding shedding characteristics is relevant for public health interventions. Viral shedding is influenced by biological characteristics of the virus, host factors and pre-existing immunity (previous infection or vaccination) of the infected individual. Although the process of human-to-human transmission is multifactorial, viral load substantially contributed to human-to-human transmission, with higher viral load posing a greater risk for onward transmission. Emerging SARS-CoV-2 variants of concern have further complicated the picture of virus shedding. As underlying immunity in the population through previous infection, vaccination or a combination of both has rapidly increased on a global scale after almost 3 years of the pandemic, viral shedding patterns have become more distinct from those of ancestral SARS-CoV-2. Understanding the factors and mechanisms that influence infectious virus shedding and the period during which individuals infected with SARS-CoV-2 are contagious is crucial to guide public health measures and limit transmission. Furthermore, diagnostic tools to demonstrate the presence of infectious virus from routine diagnostic specimens are needed.

Abstract

A better understanding of the transmission of SARS-CoV-2 is essential to inform public health measures. In this Review, Puhach, Meyer and Eckerle explore insights into what influences SARS-CoV-2 shedding, how this drives transmission and the tools available to measure this and determine infectiousness.

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Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine

Lindsey Baden, Hana El Sahly, Brandon Essink … (2020)

Abstract Background Vaccines are needed to prevent coronavirus disease 2019 (Covid-19) and to protect persons who are at high risk for complications. The mRNA-1273 vaccine is a lipid nanoparticle–encapsulated mRNA-based vaccine that encodes the prefusion stabilized full-length spike protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes Covid-19. Methods This phase 3 randomized, observer-blinded, placebo-controlled trial was conducted at 99 centers across the United States. Persons at high risk for SARS-CoV-2 infection or its complications were randomly assigned in a 1:1 ratio to receive two intramuscular injections of mRNA-1273 (100 μg) or placebo 28 days apart. The primary end point was prevention of Covid-19 illness with onset at least 14 days after the second injection in participants who had not previously been infected with SARS-CoV-2. Results The trial enrolled 30,420 volunteers who were randomly assigned in a 1:1 ratio to receive either vaccine or placebo (15,210 participants in each group). More than 96% of participants received both injections, and 2.2% had evidence (serologic, virologic, or both) of SARS-CoV-2 infection at baseline. Symptomatic Covid-19 illness was confirmed in 185 participants in the placebo group (56.5 per 1000 person-years; 95% confidence interval [CI], 48.7 to 65.3) and in 11 participants in the mRNA-1273 group (3.3 per 1000 person-years; 95% CI, 1.7 to 6.0); vaccine efficacy was 94.1% (95% CI, 89.3 to 96.8%; P<0.001). Efficacy was similar across key secondary analyses, including assessment 14 days after the first dose, analyses that included participants who had evidence of SARS-CoV-2 infection at baseline, and analyses in participants 65 years of age or older. Severe Covid-19 occurred in 30 participants, with one fatality; all 30 were in the placebo group. Moderate, transient reactogenicity after vaccination occurred more frequently in the mRNA-1273 group. Serious adverse events were rare, and the incidence was similar in the two groups. Conclusions The mRNA-1273 vaccine showed 94.1% efficacy at preventing Covid-19 illness, including severe disease. Aside from transient local and systemic reactions, no safety concerns were identified. (Funded by the Biomedical Advanced Research and Development Authority and the National Institute of Allergy and Infectious Diseases; COVE ClinicalTrials.gov number, NCT04470427.)

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Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR

Victor M Corman, Olfert Landt, Marco Kaiser … (2020)

Background The ongoing outbreak of the recently emerged novel coronavirus (2019-nCoV) poses a challenge for public health laboratories as virus isolates are unavailable while there is growing evidence that the outbreak is more widespread than initially thought, and international spread through travellers does already occur. Aim We aimed to develop and deploy robust diagnostic methodology for use in public health laboratory settings without having virus material available. Methods Here we present a validated diagnostic workflow for 2019-nCoV, its design relying on close genetic relatedness of 2019-nCoV with SARS coronavirus, making use of synthetic nucleic acid technology. Results The workflow reliably detects 2019-nCoV, and further discriminates 2019-nCoV from SARS-CoV. Through coordination between academic and public laboratories, we confirmed assay exclusivity based on 297 original clinical specimens containing a full spectrum of human respiratory viruses. Control material is made available through European Virus Archive – Global (EVAg), a European Union infrastructure project. Conclusion The present study demonstrates the enormous response capacity achieved through coordination of academic and public laboratories in national and European research networks.

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Virological assessment of hospitalized patients with COVID-2019

Roman Wölfel, Victor M Corman, Wolfgang Guggemos … (2020)

Coronavirus disease 2019 (COVID-19) is an acute infection of the respiratory tract that emerged in late 20191,2. Initial outbreaks in China involved 13.8% of cases with severe courses, and 6.1% of cases with critical courses3. This severe presentation may result from the virus using a virus receptor that is expressed predominantly in the lung2,4; the same receptor tropism is thought to have determined the pathogenicity-but also aided in the control-of severe acute respiratory syndrome (SARS) in 20035. However, there are reports of cases of COVID-19 in which the patient shows mild upper respiratory tract symptoms, which suggests the potential for pre- or oligosymptomatic transmission6-8. There is an urgent need for information on virus replication, immunity and infectivity in specific sites of the body. Here we report a detailed virological analysis of nine cases of COVID-19 that provides proof of active virus replication in tissues of the upper respiratory tract. Pharyngeal virus shedding was very high during the first week of symptoms, with a peak at 7.11 × 108 RNA copies per throat swab on day 4. Infectious virus was readily isolated from samples derived from the throat or lung, but not from stool samples-in spite of high concentrations of virus RNA. Blood and urine samples never yielded virus. Active replication in the throat was confirmed by the presence of viral replicative RNA intermediates in the throat samples. We consistently detected sequence-distinct virus populations in throat and lung samples from one patient, proving independent replication. The shedding of viral RNA from sputum outlasted the end of symptoms. Seroconversion occurred after 7 days in 50% of patients (and by day 14 in all patients), but was not followed by a rapid decline in viral load. COVID-19 can present as a mild illness of the upper respiratory tract. The confirmation of active virus replication in the upper respiratory tract has implications for the containment of COVID-19.

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Author and article information

Contributors

Isabella Eckerle:

ORCID: http://orcid.org/0000-0002-4850-7172

Isabella.Eckerle@unige.ch

Journal

Journal ID (nlm-ta): Nat Rev Microbiol

Journal ID (iso-abbrev): Nat Rev Microbiol

Title: Nature Reviews. Microbiology

Publisher: Nature Publishing Group UK (London )

ISSN (Print): 1740-1526

ISSN (Electronic): 1740-1534

Publication date (Electronic): 2 December 2022

Pages: 1-15

Affiliations

[1 ]GRID grid.8591.5, ISNI 0000 0001 2322 4988, Department of Medicine, Faculty of Medicine, , University of Geneva, ; Geneva, Switzerland

[2 ]GRID grid.8591.5, ISNI 0000 0001 2322 4988, Centre for Vaccinology, Department of Pathology and Immunology, , University of Geneva, ; Geneva, Switzerland

[3 ]GRID grid.150338.c, ISNI 0000 0001 0721 9812, Geneva Centre for Emerging Viral Diseases, , Geneva University Hospitals, ; Geneva, Switzerland

[4 ]GRID grid.150338.c, ISNI 0000 0001 0721 9812, Division of Infectious Diseases, , Geneva University Hospitals, ; Geneva, Switzerland

Author information

Olha Puhach http://orcid.org/0000-0002-5789-8988

Benjamin Meyer http://orcid.org/0000-0003-0601-3550

Isabella Eckerle http://orcid.org/0000-0002-4850-7172

Article

Publisher ID: 822

DOI: 10.1038/s41579-022-00822-w

PMC ID: 9716513

PubMed ID: 36460930

SO-VID: 4f469fec-f23c-4aa0-b7af-12a6942d80c6

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This article is made available via the PMC Open Access Subset for unrestricted research re-use and secondary analysis in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.

SARS-CoV-2 viral load and shedding kinetics

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Novel Coronavirus Disease COVID-19

Most cited references 206

Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine

Detection of 2019 novel coronavirus (2019-nCoV) by real-time RT-PCR

Virological assessment of hospitalized patients with COVID-2019

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