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Viral Emissions into the Air and Environment after SARS-CoV-2 Human Challenge: A Phase 1, Open Label, First-in-Human Study
33 Pages Posted: 16 Dec 2022
More...Abstract
Background: Effectively implementing strategies to curb SARS-CoV-2 transmission requires understanding who is contagious and when. Whilst viral load (VL) on upper respiratory swabs has commonly been used to infer contagiousness, measuring viral emissions may be more accurate to indicate the chance of onward transmission and identify likely routes. SARS-CoV-2 human challenge involves intentional inoculation of volunteers with a standardised dose and route of the same virus, providing opportunities to sample intensely across the whole course of infection including in the pre-symptomatic period.
Methods: Following intranasal challenge of 36 volunteers with wild-type SARS-CoV-2, viral emissions were collected using an air sampler, adapted facemasks, hand and surface swabs, and subjected to virological analyses.
Findings: Eighteen volunteers became infected and emitted large quantities of virus. Viable SARS-CoV-2 was collected from breath captured in facemasks and from surfaces, including small frequently-touched surfaces and larger surfaces where airborne virus could deposit. Viral emissions correlated more strongly with VL in nasal swabs than throat swabs. Two individuals emitted 86% of airborne virus, and the majority of airborne virus collected was released on a few days. Individuals who reported the highest symptom scores were not those who emitted most virus. Very few emissions occurred before the first reported symptom (7%) and hardly any before the first positive lateral flow antigen test (2%).
Interpretation: After controlled experimental inoculation, the timing, extent and routes of viral emissions was heterogeneous. We observed a minority of high airborne virus emitters, giving support to the notion of superspreading individuals or events. Our data implicates the nose as the most important source of emissions. Frequent self-testing coupled with isolation upon awareness of first symptoms could reduce onward transmissions.
Funding: PROTECT COVID-19 National Core Study on Transmission and the Environment. The authors also gratefully acknowledge support from the UK Vaccine Taskforce of the Department of Business, Energy and Industrial Strategy of Her Majesty’s Government (BEIS). AS is supported by a National Institute for Health Research (NIHR) academic clinical lectureship. CC and AS are supported by the NIHR Imperial Biomedical Research Centre (BRC) award to Imperial College Healthcare NHS Trust and Imperial College London. The authors would like to acknowledge Anika Wisniewska, Eve Fletcher and Baber Saleem for preparing the sampling masks. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, BEIS.
Declaration of Interests: We have no conflicts of interest to disclose.
Ethics Approval Statement: This study was approved by the UK Health Research Authority Ad Hoc Specialist Ethics Committee (reference: 20/UK/0002). Written informed consent was obtained from volunteers prior to screening and enrolment.
Keywords: SARS-CoV-2, human challenge, transmission, virus emission, airborne, fomite
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