Evolution of SARS-CoV-2 Shedding in Exhaled Breath Aerosols

KRISTEN K. COLEMAN, Jianyu Lai, Sheldon Tai, Jennifer German, Filbert Hong, Barbara J. Albert, Yi Esparza, Aditya Kiran Srikakulapu, Maria Schanz, Isabel Sierra Maldonado, Molly Oertel, Naja Fadul, Louie Gold, Stuart Weston, Kathleen McPhaul, Matthew B. Frieman, Donald K. Milton, University of Maryland School of Public Health

     Abstract Number: 455
     Working Group: Aerosol Science of Infectious Diseases: What We Have Learned and Still Need to Know about Transmission, Prevention, and the One Health Concept

Abstract
Transmissibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to increase as new variants emerge. Is increased transmissibility associated with increased viral aerosol shedding? From June 2020 through March 2022, we collected exhaled breath aerosol (EBA) samples from 93 volunteers (ages 6-66) with mostly mild SARS-CoV-2 infections. A Gesundheit-II was used to collect fine (≤5 μm in diameter) and coarse (>5 μm) EBA using a 30-minute loud speaking/singing protocol. Samples were assayed using TaqPath COVID-19 Real-Time RT-PCR Assay (Thermo Scientific) and cultured using TMPRSS2-expressing VeroE6 cells and A549-ACE2 cells. SARS-CoV-2 RNA was detected in EBA from 44 (47%) of the participants. Infectious SARS-CoV-2 was recovered from EBA of six participants, including one B.1.2, one Alpha, two Delta, and four Omicron infections, three of whom were singly boosted. Infectious virus was recovered from seven fine and one coarse EBA sample. All Delta and Omicron cases were fully vaccinated (63% boosted). The strongest predictors of fine EBA viral RNA load were SARS-CoV-2 variant, systemic symptom score, saliva viral RNA load, age, and coughs during collection. Overall, fine EBA viral RNA loads were similar for Alpha, Delta, and Omicron. No significant difference in EBA load was observed between Omicron subvariants (BA.1, BA.1.1, and BA.2); the maximum was 1.8x10⁷ RNA copies of Omicron BA.1.1. Alpha, Delta, and Omicron are associated with increased viral shedding in fine EBA, compared with ancestral strains and variants not associated with increased transmissibility. Evolutionary selection for immune evasion and high viral aerosol shedding appears to be occurring. Because vaccination and boosting cannot prevent shedding of infectious virus via aerosols, non-pharmaceutical interventions including ventilation, filtration, and germicidal UV air disinfection are still needed to mitigate COVID-19 transmission and protect vulnerable populations.