Adenaiye, Oluwasanmi O.Lai, JianyuBueno de Mesquita, P. JacobHong, FilbertYoussefi, SomayehGerman, JenniferTai, S.H. SheldonAlbert, BarbaraSchanz, MariaWeston, StuartHang, JunFung, ChristianChung, Hye KyungColeman, Kristen K.Sapoval, NicolaeTreangen, ToddBerry, Irina MaljkovicMullins, KristinFrieman, MatthewMa, TianzhouMilton, Donald K.University of Maryland StopCOVID Research Group2022-09-292022-09-292022Adenaiye, Oluwasanmi O., Lai, Jianyu, Bueno de Mesquita, P. Jacob, et al.. "Infectious Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Exhaled Aerosols and Efficacy of Masks During Early Mild Infection." <i>Clinical Infectious Diseases,</i> 75, no. 1 (2022) Oxford University Press: e241-e248. https://doi.org/10.1093/cid/ciab797.https://hdl.handle.net/1911/113440Severe 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.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.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 µm), 26% of coarse (&gt;5 µm) 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.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.engThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.Journal articleciab797https://doi.org/10.1093/cid/ciab797