Airborne transmission of SARS-CoV-2
There is overwhelming evidence that inhalation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) represents a major transmission route for coronavirus disease 2019 (COVID-19). There is an urgent need to harmonize discussions about modes of virus transmission across disciplines to ensure the most effective control strategies and provide clear and consistent guidance to the public. To do so, we must clarify the terminology to distinguish between aerosols and droplets using a size threshold of 100 µm, not the historical 5 µm (1). This size more effectively separates their aerodynamic behavior, ability to be inhaled, and efficacy of interventions.
Viruses in droplets (larger than 100 µm) typically fall to the ground in seconds within 2 m of the source and can be sprayed like tiny cannonballs onto nearby individuals. Because of their limited travel range, physical distancing reduces exposure to these droplets. Viruses in aerosols (smaller than 100 µm) can remain suspended in the air for many seconds to hours, like smoke, and be inhaled. They are highly concentrated near an infected person, so they can infect people most easily in close proximity. But aerosols containing infectious virus (2) can also travel more than 2 m and accumulate in poorly ventilated indoor air, leading to superspreading events (3).
Individuals with COVID-19, many of whom have no symptoms, release thousands of virus-laden aerosols and far fewer droplets when breathing and talking (4–6). Thus, one is far more likely to inhale aerosols than be sprayed by a droplet (7), and so the balance of attention must be shifted to protecting against airborne transmission. In addition to existing mandates of mask-wearing, social distancing, and hygiene efforts, we urge public health officials to add clear guidance about the importance of moving activities outdoors, improving indoor air using ventilation and filtration, and improving protection for high-risk workers (8).
References and Notes
1
The National Academies of Sciences, Engineering, and Medicine, “Video 31—CQ1 reflection and syntheses: Identifying opportunities and gaps on the path ahead by Kim Prather” (Airborne Transmission of SARSCoV-2: A Virtual Workshop, 26 to 27 August 2020); www.nationalacademies.org/event/08-26-2020/airborne-transmission-of-sars-cov-2-a-virtual-workshop.
2
J. A. Lednicky et al., Int. J. Infect. Dis., 10.1016/j.ijid.2020.09.025 (2020).
3
S. L. Miller et al., Indoor Air, 10.1111/ina.12751 (2020).
4
K. A. Prather, C. C. Wang, R. T. Schooley, Science 368, 1422 (2020).
5
V. Stadnytskyi, C. E. Bax, A. Bax, P. Anfinrud, Proc. Natl. Acad. Sci. U.S.A. 117, 11875 (2020).
6
J. Ma et al., Clin. Infect. Dis., 10.1093/cid/ciaa1283 (2020).
7
W. Chen et al.Build. Environ. 176, 106859 (2020).
8
L. Morawska et al., Environ. Int. 142, 105832 (2020).
Competing Interests
K.A.P. is Director of the National Science Foundation Center for Aerosol Impacts on Chemistry of the Environment. L.C.M. is a member of the Science Advisory Board and holds stock options for Phylagen and is a paid reviewer for the Alfred P. Sloan Foundation. R.T.S. is a member of the Gilead Sciences Scientific Advisory Board and chairs Data Safety and Monitoring Boards for VIR, Gilead, and Merck. Honoraria for these activities are paid to the Regents of the University of California. R.T.S. has served as a scientific consultant to Pfizer and to AbbVie. M.A.M. is the unpaid Chair of the National Academy of Medicine Committee on Personal Protective Equipment for Workplace Safety and Health.
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Science
Volume 370 | Issue 6514
16 October 2020
16 October 2020
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Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
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Published in print: 16 October 2020
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Competing Interests
K.A.P. is Director of the National Science Foundation Center for Aerosol Impacts on Chemistry of the Environment. L.C.M. is a member of the Science Advisory Board and holds stock options for Phylagen and is a paid reviewer for the Alfred P. Sloan Foundation. R.T.S. is a member of the Gilead Sciences Scientific Advisory Board and chairs Data Safety and Monitoring Boards for VIR, Gilead, and Merck. Honoraria for these activities are paid to the Regents of the University of California. R.T.S. has served as a scientific consultant to Pfizer and to AbbVie. M.A.M. is the unpaid Chair of the National Academy of Medicine Committee on Personal Protective Equipment for Workplace Safety and Health.
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RE: Aerosol Transmission of SARS-CoV-2
Transmission of the SARS-CoV-2 virus that causes COVID-19 should be of immense concern to every healthcare worker who relies on PPE as that might not be safe and effective in the face of airborne transmissions in both confined and open spaces.
Comprehensive discussions of the transmission of COVID-19 by droplets and the lighter evaporating aerosols are presented in Jayaweera et al. (2020) and Klompas, Baker and Rhee (2020).
As shown in Zeng, Wang, Li et al. (2020), the SARS-CoV-2 virus can be carried by aerosols that remain suspended in the air and carried by currents, so that social distancing norms will be ineffective in preventing infection.
In short, medical masks, face shields, social distancing, and the wearing of eyeglasses might not provide adequate protection against infection by the SARS-CoV-2 virus.
References
Jayaweera, M., H. Perera, B. Gunawardana and J. Manatunge (2020), Transmission of COVID-19 virus by droplets and aerosols: A critical review on the unresolved dichotomy, Environmental Research, 88, September 2020, published online 2020 June 13, doi: 10.1016/j.envres.2020.109819. https://www.sciencedirect.com/science/article/pii/S0013935120307143?via%...
WHO COVID-19 Global literature on coronavirus disease https://search.bvsalud.org/global-literature-on-novel-coronavirus-2019-n...
Klompas, M., M.A. Baker and C. Rhee (2020), Airborne Transmission of SARS-CoV-2 - Theoretical Considerations and Available Evidence, Journal of the American Medical Association(JAMA), published online 13 July 2020, doi:10.1001/jama.2020.12458.
https://jamanetwork.com/journals/jama/fullarticle/2768396
WHO COVID-19 Global literature on coronavirus diseasehttps://search.bvsalud.org/global-literature-on-novel-coronavirus-2019-n...
Zeng, W.B., X.L. Wang, J.Y. Li et al. (2020), Association of Daily Wear of Eyeglasses With Susceptibility to Coronavirus Disease 2019 Infection, Journal of the American Medical Association (JAMA) Ophthalmology, doi:10.1001/jamaophthalmol.2020.3906, published online 16 September 2020.
https://jamanetwork.com/journals/jamaophthalmology/fullarticle/2770872
WHO COVID-19 Global literature on coronavirus disease
https://search.bvsalud.org/global-literature-on-novel-coronavirus-2019-n...
Expert scientists should know the past lessons from SARS and MERS
Kimberly A. Prather et al. wrote a letter published in Science on Oct. 16 in 2020 (1). Why do they talk about the fact now as of Oct. 16 in 2020. SARS-CoV-2 uses human ACE2 as entry receptor which was discovered and published on April 8 in 2020 and published online 2020 March 5 (2). Both SARS-CoV and SARS-CoV-2 use the same ACE2 entry receptor and human proteases as entry activators (2). This deduces that the COVID-19 infection transmission is the same as SARS.
SARS-CoV-2 was named after SARS by WHO on Feb. 11 2020 (3). This virus naming means that SARS-CoV-2 is very similar to SARS-COV.
Expert scientists must know the past lessons learned from SARS and MERS which should be utilized for mitigating the COVID-19 pandemic. Two facts from SARS are summarized as follows:
1. SARS is an airborne virus and can spread through small droplets of saliva in a similar way to the cold and influenza. It was the first severe and readily transmissible new disease to emerge in the 21st century and showed a clear capacity to spread along the routes of international air travel (3). The important fact of SARS airborne virus has been supported by four papers (4,5,6,7).
2. SARS is an asymptomatic infection disease (8,9,10,11,12,13).
Conclusion
We must use the past lessons for mitigating the COVID-19 pandemic. On March 5 in 2020 expert scientists knew that COVID-19 is an airborne virus.
References:
1.Kimberly A. Prather et al., Airborne transmission of SARS-CoV-2, Science 16 Oct 2020 Vol. 370, Issue 6514, pp. 303-304 DOI: 10.1126/science.abf0521
2. Mahmoud Gheblawi et al, Angiotensin-Converting Enzyme 2: SARS-CoV-2 Receptor and Regulator of the Renin-Angiotensin System, Circulation Research. 2020;126:1456–1474, https://doi.org/10.1161/CIRCRESAHA.120.317015
3. WHO, Severe Acute Respiratory Syndrome (SARS),
https://www.who.int/health-topics/severe-acute-respiratory-syndrome
4. N Engl J Med 2004; 350:1731-1739 DOI: 10.1056/NEJMoa032867
5. Timothy F. Booth et al., Detection of Airborne Severe Acute Respiratory Syndrome (SARS) Coronavirus and Environmental Contamination in SARS Outbreak Units, The Journal of Infectious Diseases, Volume 191, Issue 9, 1 May 2005, Pages 1472–1477, https://doi.org/10.1086/429634
6. Xiao S, Li Y, Wong T-w, Hui DSC (2017) Role of fomites in SARS transmission during the largest hospital outbreak in Hong Kong.
PLoS ONE 12(7): e0181558. https://doi.org/10.1371/journal.pone.0181558
7. Hagbom, M., Nordgren, J., Nybom, R. et al. Ionizing air affects influenza virus infectivity and prevents airborne-transmission. Sci Rep 5, 11431 (2015).
https://doi.org/10.1038/srep11431
8. Lee HK, Tso EY, Chau TN, et al. Asymptomatic Severe Acute Respiratory Syndrome–associated Coronavirus Infection.
Emerging Infectious Diseases. 2003;9(11):1491-1492. doi:10.3201/eid0911.030401.
9. Wilder-Smith A., Teleman M.D., Heng B.H., Earnest A., Ling A.E. Asymptomatic SARS coronavirus infection among healthcare workers, Singapore.
Emerg Infect Dis. 2005;11:1142–1145.
10. Rainer TH et al. The spectrum of severe acute respiratory syndrome-associated coronavirus infection.
Ann Intern Med 2004 Apr 20; 140:614-9.
11. Xiao-yan Che et al., A Patient with Asymptomatic Severe Acute Respiratory Syndrome (SARS) and Antigenemia from the 2003–2004 Community Outbreak of SARS in Guangzhou, China, Clinical Infectious Diseases, Volume 43, Issue 1, 1 July 2006, Pages e1–e5, https://doi.org/10.1086/504943
12. Consensus document on the epidemiology of severe acute respiratory syndrome (SARS), WHO, https://www.who.int/csr/sars/WHOconsensus.pdf?ua=1
13. Cherry, J., Krogstad, P. SARS: The First Pandemic of the 21st Century. Pediatr Res 56, 1–5 (2004). https://doi.org/10.1203/01.PDR.0000129184.87042.FC
RE: The principles of fluid mechanics answers the airborne transmission
Recent studies have highlighted that in indoor settings the virus can remain airborne for more than six feet . A cough or a sneeze produces what is described as a "multiphase, turbulent puff cloud" that boils and expands as it spreads. Because exhaled air is typically warmer and moister than room air, it billows up to the ceiling, carrying with it a continuum of different-sized snot particles Some of these airborne particles can either be directly inhaled or end up in the eyes, which connect to the nose and respiratory tract via our tear ducts. Given the virus' 'freshness' in this wham-bam scenario, this is the most direct and contagious way of catching a viral bug. By the way, a surgical mask seems to be a more effective deterrent when worn by the infected, not the healthy. In outside scenario, at wind speeds from 4 km/h to 15 km/h, saliva droplets can travel to distances up to 6 m with a decrease in concentration and liquid droplet size in the wind direction. Once the particles fall from the cloud and settle on public surfaces like door handles, countertops, keyboards etc., remains dependent on human hands for any further transportation. Because hand washing is neither perfect nor perpetual, viral inoculation can be abolished by keeping hands away from eyes, nose, and mouth. The issues arising from the past and the recent pandemic require a holistic approach to elucidate the open scientific questions and address the practical challenges. Such an approach would require closer interaction between bio-medicine, engineering fluid physics, and social sciences till that time the airborne transmission is debatable. Understanding this mode of transmission can inform and modulate public health interventions to minimise the disease risk.