Infectious Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Exhaled Aerosols and Efficacy of Masks During Early Mild Infection

Exhaled SARS-CoV-2 aerosols are infectious and evolution is favoring more efficient aerosol generation. Loose-fitting masks moderately reduce viral aerosol release indicating that ventilation, filtration, UV air sanitation, and tight-fitting masks are needed to protect vulnerable people in public-facing jobs and indoor spaces. Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) epidemiology implicates airborne transmission; aerosol infectiousness and impacts of masks and variants on aerosol shedding are not well understood. Methods We recruited coronavirus disease 2019 (COVID-19) cases to give blood, saliva, mid-turbinate and fomite (phone) swabs, and 30-minute breath samples while vocalizing into a Gesundheit-II, with and without masks at up to 2 visits 2 days apart. We quantified and sequenced viral RNA, cultured virus, and assayed serum samples for anti-spike and anti-receptor binding domain antibodies. Results We enrolled 49 seronegative cases (mean days post onset 3.8 +/- 2.1), May 2020 through April 2021. We detected SARS-CoV-2 RNA in 36% of fine (<= 5 mu m), 26% of coarse (>5 mu m) aerosols, and 52% of fomite samples overall and in all samples from 4 alpha variant cases. Masks reduced viral RNA by 48% (95% confidence interval [CI], 3 to 72%) in fine and by 77% (95% CI, 51 to 89%) in coarse aerosols; cloth and surgical masks were not significantly different. The alpha variant was associated with a 43-fold (95% CI, 6.6- to 280-fold) increase in fine aerosol viral RNA, compared with earlier viruses, that remained a significant 18-fold (95% CI, 3.4- to 92-fold) increase adjusting for viral RNA in saliva, swabs, and other potential confounders. Two fine aerosol samples, collected while participants wore masks, were culture-positive. Conclusions SARS-CoV-2 is evolving toward more efficient aerosol generation and loose-fitting masks provide significant but only modest source control. Therefore, until vaccination rates are very high, continued layered controls and tight-fitting masks and respirators will be necessary.

Automated summary

Exhaled SARS-CoV-2 aerosols are infectious and the virus is evolving to generate more efficient aerosols. Loose-fitting masks can moderately reduce viral aerosol release, but to protect vulnerable individuals in public-facing jobs and indoor spaces, ventilation, filtration, UV air sanitation, and tight-fitting masks are needed.