Prather, Kimberly A., Marr, Linsey C. et al. 2020. “Airborne transmission of SARS-CoV-2.” Science Vol. 370, Issue 6514, pp. 303-304. 16 Oct 2020.

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).

https://science.sciencemag.org/content/370/6514/303.2

NOTES: published as an open letter to the scientific community by top scientists from research universities across the USA

Authors of the Letter:
Kimberly A. Prather1,*, Linsey C. Marr2,*, Robert T. Schooley3, Melissa A. McDiarmid4, Mary E. Wilson5,6, Donald K. Milton7
1Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037, USA.
2Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA 24061, USA.
3Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA.
4Division of Occupational & Environmental Medicine, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
5School of Medicine, University of California, San Francisco, CA 94143, USA.
6Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA.
7Institute for Applied Environmental Health, University of Maryland, College Park, MD 20742, USA.

Science 16 Oct 2020:
Vol. 370, Issue 6514, pp. 303-304
DOI: 10.1126/science.abf0521