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Infectious viral load in unvaccinated and vaccinated individuals infected with ancestral, Delta or Omicron SARS-CoV-2.
Puhach, Olha; Adea, Kenneth; Hulo, Nicolas; Sattonnet, Pascale; Genecand, Camille; Iten, Anne; Jacquérioz, Frédérique; Kaiser, Laurent; Vetter, Pauline; Eckerle, Isabella; Meyer, Benjamin.
  • Puhach O; Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
  • Adea K; Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
  • Hulo N; Service for Biomathematical and Biostatistical Analyses, Institute of Genetics and Genomics, University of Geneva, Geneva, Switzerland.
  • Sattonnet P; Department of Microbiology and Molecular Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
  • Genecand C; Cantonal Health Service, General Directorate for Health, Geneva, Switzerland.
  • Iten A; Service of Prevention and Infection Control, Directorate of Medicine and Quality, Geneva University Hospitals, Geneva, Switzerland.
  • Jacquérioz F; Geneva Centre for Emerging Viral Diseases, Geneva University Hospitals, Geneva, Switzerland.
  • Kaiser L; Division of Tropical and Humanitarian Medicine, Geneva University Hospitals, Geneva, Switzerland.
  • Vetter P; Primary Care Division, Geneva University Hospitals, Geneva, Switzerland.
  • Eckerle I; Geneva Centre for Emerging Viral Diseases, Geneva University Hospitals, Geneva, Switzerland.
  • Meyer B; Laboratory of Virology, Division of Laboratory Medicine, Geneva University Hospitals & Faculty of Medicine, University of Geneva, Geneva, Switzerland.
Nat Med ; 28(7): 1491-1500, 2022 07.
Article in English | MEDLINE | ID: covidwho-1784006
ABSTRACT
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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Full text: Available Collection: International databases Database: MEDLINE Main subject: SARS-CoV-2 / COVID-19 Type of study: Diagnostic study / Prognostic study Topics: Vaccines / Variants Limits: Humans Language: English Journal: Nat Med Journal subject: Molecular Biology / Medicine Year: 2022 Document Type: Article Affiliation country: S41591-022-01816-0

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Full text: Available Collection: International databases Database: MEDLINE Main subject: SARS-CoV-2 / COVID-19 Type of study: Diagnostic study / Prognostic study Topics: Vaccines / Variants Limits: Humans Language: English Journal: Nat Med Journal subject: Molecular Biology / Medicine Year: 2022 Document Type: Article Affiliation country: S41591-022-01816-0