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Aerosol inhalation is increasingly well recognized as a major if not primary mode of transmission of SARS-CoV-21,2. Over the course of the COVID-19 pandemic, three highly transmissible lineages evolved and became globally dominant3. One hypothesis to explain increased transmissibility is that natural selection favours variants with higher rates of viral aerosol shedding. However, the extent of aerosol shedding of successive SARS-CoV-2 variants is unknown. Here, we demonstrate that viral shedding (measured as RNA copies) into exhaled breath aerosol was significantly greater during infections with Alpha, Delta, and Omicron than with ancestral strains and variants not associated with increased transmissibility. The three highly transmissible variants independently evolved a high viral aerosol shedding phenotype, demonstrating convergent evolution. We did not observe statistically significant differences in rates of shedding between Alpha, Delta, and Omicron infections. The highest shedder in our study, however, had an Omicron infection and shed three orders of magnitude more viral RNA copies than the maximum observed for Delta and Alpha4. Our results also show that fully vaccinated and boosted individuals, when infected, can shed infectious SARS-CoV-2 via exhaled breath aerosols. These findings provide additional evidence that inhalation of infectious aerosols is the dominant mode of transmission and emphasize the importance of ventilation, filtration, and air disinfection to mitigate the pandemic and protect vulnerable populations. We anticipate that monitoring aerosol shedding from new SARS-CoV-2 variants and emerging pathogens will be an important component of future threat assessments and will help guide interventions to prevent transmission via inhalation exposure.
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BackgroundSARS-CoV-2 epidemiology implicates airborne transmission; aerosol infectiousness and impacts of masks and variants on aerosol shedding are not well understood. MethodsWe recruited 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 two visits two days apart. We quantified and sequenced viral RNA, cultured virus, and assayed sera for anti-spike and anti-receptor binding domain antibodies. ResultsWe enrolled 49 seronegative cases (mean days post onset 3.8 {+/-}2.1), May 2020 through April 2021. We detected SARS-CoV-2 RNA in 45% of fine ([≤]5 {micro}m), 31% of coarse (>5 {micro}m) aerosols, and 65% of fomite samples overall and in all samples from four 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. ConclusionSARS-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. Key PointsO_LICases exhale infectious viral aerosols C_LIO_LISARS-CoV-2 evolution favors more efficient aerosol generation. C_LIO_LILoose-fitting masks moderately reduce viral RNA aerosol. C_LIO_LIVentilation, filtration, UV air sanitation, and tight-fitting masks are needed to protect vulnerable people in public-facing jobs and indoor spaces. C_LI
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OBJECTIVESTo investigate if COVID-19 convalescent plasma (CCP) transfusion in patients with severe respiratory failure will increase plasma levels of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) antibody titers while improving survival and clinical outcomes. DESIGNObservational, retrospective, control study of anti-Receptor binding domain (RBD) of SARS-CoV-2 IgG and IgM titers from serial plasma samples drawn before and after CCP administration. Clinical improvement in CCP recipients is assessed and compared to COVID-19 control patients. SETTINGPatients hospitalized with severe COVID19, United States, between April 17 and July 19, 2020 PARTICIPANTS34 patients hospitalized with severe or life threatening COVID-19 and who consented and received a CCP transfusion, 95 control patients with COVID-19 not transfused with CCP. 34 out the 95 control patients were matched for age, sex, and the level of respiratory support required. Patients less than 18 years old were excluded. MAIN OUTCOME MEASURESSerial trends of anti-RBD of SARS-CoV-2 IgG and IgM titers in CCP recipients are compared to those in control patients. The primary outcome is survival at 30 days, and the secondary outcomes are length of ventilatory and/or extracorporeal membrane oxygenation (ECMO) support, length of stay (LOS) in the hospital, and LOS in the ICU. RESULTSCCP transfusion occurred in 34 patients at a median of 12 days following COVID-19 symptom onset. Immediately prior to CCP transfusion, patients median anti-RBD SARS-CoV-2 IgG and IgM titers were 1:3200 (IQR, 1:50 to 1:9600) and 1:320 (IQR, 1:40 to 1:640) respectively. Following a Loess regression analysis, the kinetics and distribution of anti-RBD of SARS-CoV-2 IgG and IgM in plasma from CCP recipients were comparable to those from a control group of 68 patients who did not receive CCP. CCP recipients presented with similar survival, similar duration on ventilatory and/or ECMO support, as well as ICU and hospital LOS, compared to a matched control group of 34 patients. CONCLUSIONIn the present study, hospitalized COVID-19 patients with severe respiratory failure transfused with CCP presented with high titers of SARS-CoV-2 IgG antibodies before transfusion and did not show improved survival at 30 days.
