COVID-19: Is It airborne?

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Before its official naming, COVID-19 caused by SARS-CoV-2 emerged in Wuhan city, China. In the months that followed, the new coronavirus strain continues to ravage the unprepared world.  

From citywide lockdown, travel restrictions, infections aboard cruise ships, social distancing to the closing of schools and businesses, the world scrambles to combat COVID-19. 

More than 85,000 people have perished from COVID-19, with over 1.4 million confirmed cases worldwide. At least 200 countries and territories are now affected, with the U.S. leading the chart followed by European countries, Spain, Italy, Germany, and France. 

Every day, the world is watching the worrying news closely as the numbers continue to climb. 

Since the start of the pandemic, most world leaders, health organizations, and experts have advised against the use of face masks for the healthy general public. Only healthcare workers, people who are unwell or caring for the sick and vulnerable are encouraged to wear a face mask as a preventative measure. 

However, some countries have advised the opposite, urging everyone to mask up when venturing outside the safety of their own homes. CDC has reversed its previous advice on face mask use and now recommending the public to mask up using cloth face covering.

Credit: CDC

The reversal of face mask policy by CDC was partly due to the concern of plausible airborne transmission of SARS-CoV-2.  

How SARS-CoV-2 transmit?

Both CDC and WHO have confirmed that the spread of COVID-19 is through respiratory droplets from the nose or mouth of an infected person. Surrounding people can contract the virus if these droplets reach their eye, nose, and mouth.

Photo by Sam Hollingworth

Visible respiratory droplets forcefully expelled from a sneeze or cough are often heavy enough and will fall immediately onto surrounding objects and surfaces. When another person touches a contaminated surface or object, called fomite (doorknob, phone, utensil, etc.), the viruses get transferred to his/her hands. The person then contracts the disease by touching their face (eyes, nose, and mouth) with dirty hands.

A recent study has shown that the SARS-CoV-2 virus can survive on surfaces from 24 to 72 hours depending on the nature of surfaces such as plastic and steel.

This is why the World Health Organisation (WHO) urges everyone to keep a distance of at least 1 meter or 3 feet from a sick person and wash your hands frequently. Regular cleaning of high-traffic surfaces in your household and good hand hygiene goes a long way in minimizing the chances of viruses lingering around. 

Is 1-meter distance enough? If you ever had an explosive sneeze, you would know that 1 meter isn’t good enough. According to one study, respiratory droplets from a sneeze can travel a greater distance, around 6 meters away and at a velocity of 50m/s (equivalent to180km/h or over 100miles/h) indoor.

High speed footage courtesy of Lydia Bourouiba, The Fluid Dynamics of Disease Transmission Laboratory, MIT

The science behind is fairly complicated. The size and movement of the droplets are affected by various variables. A sneeze produces a complex fluid cascade, it is not as simple as spraying.

A team at MIT has studied how sneezing disperses droplets showed that coughs and sneezes produce clouds of gas that carry infectious droplets that can travel farther away.

Various sizes of droplets eventually fall to the ground, but some may remain suspended in the air. What this means is that a safety distance of 1 meter may not be enough. 

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What about airborne transmission? 

Airborne transmission is different from respiratory droplets. A pathogen is considered airborne if it can be spread through aerosol particles, that are small enough (typically less than 5 µm). These particles can stay suspended in the air for a long period, hence allowing them to travel a greater distance.

The particle size is a crucial factor in play here. The diameters of the aerosol particles determine their reach into a human’s respiratory system. An aerosol particle smaller than 10 µm can enter the bronchi when inhaled. Nanoscale particles can even pass through the air-blood barrier within the lungs. 

Evidence so far

For SARS-CoV-2, a recent preliminary study showed that the virus remained viable in aerosols for up to 3 hours in the air. The study was criticized for its unrealistic artificial condition for their experiments. Other studies reported finding viral RNA from SARS-CoV-2 in air samples from various locations, including the department stores, hospital isolation rooms, and quarantine facilities.

Photo by Fusion Medical Animation on Unsplash

WHO released a statement clarifying that the scientific evidence of viral RNA in the air samples does not mean that the viruses are viable and transmissible. WHO also pointed out its study of COVID-19 cases in China did not find evidence of airborne transmission of SARS-CoV-2. 

Overall, there is simply not enough evidence for health experts and scientists to confirm that SARS-CoV-2 is airborne. It is understandable that the public is confused and questioning the progress of the science on COVID-19. 

Scientists operate on the evidence-based approach. More studies need to be conducted still. That is not necessarily indicative of incompetence. It is a scientist’s role to question the unknown, be detail-oriented, persistent, open-minded and free of bias. 

More to do

The reality is this is a new virus strain. There is a lot that we don’t know. We don’t know the infectious dose of SARS-CoV-2. How much SARS-CoV-2 particles are necessary to cause an infection? What is the number of virus particles in an aerosol particle of different sizes? Are they viable? If they are viable, then for how long and what are the mechanism of distribution in the air? Can they circulate through the air conditioning system? 

woman in black jacket wearing white mask
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Only time will tell as more studies will be conducted. No definitive conclusion can be drawn from the findings to date. 

But the lack of evidence to prove airborne transmission doesn’t mean that it is not airborne. Future data and evidence might support this notion. 

Both WHO and CDC suggest that SARS-CoV-2 is mainly transmitted through contact with respiratory droplets rather than through the air because the droplets are too heavy to remain suspended. 

Should we assume it’s airborne?

Using the word “airborne” can have very significant consequences. It can trigger panic among the public. And we have seen the consequences of panic buying and how humans can turn on each other over toilet papers. 

But avoiding this term can have dire consequences too. By assuming the possibility of airborne transmission unless enough experimental evidence can rule it out, people can take more precautions in protecting themselves. 

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It could be as simple as increasing ventilation indoors. These simple measures can help to ensure that potentially infectious aerosols can be vented out and diluted. People should also be more aware of sneezes and coughs, and cover up when possible.

Limit as many physical interactions as possible. Obey the social distancing rules, lockdown laws, quarantine measures, whatever you call it STRICTLY.

Masking up can be protective if done properly. However, everyone should not panic buy hospital-grade face masks and protective gear (PPE) as they are crucial for our healthcare workers, vulnerable populations and all front liners. 

Admittedly, some people will still panic and exhibit certain behaviors. If there is one variable that will always be hard to account for, that is human nature. 

Stand together

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But understand this, the panic buying behaviors and consequently the shortage of PPE for healthcare workers and front-liners can have direct effects on everyone. We need them to take care of us when we are sick. They are working at the frontline day-in and -out exposed to inconceivable numbers of germs and risks. 

If the hospital is a warzone and healthcare workers are the soldiers, would you send an unarmed soldier to fight a battle? PPE including face masks is the equivalent of a soldier’s armory.  

They are all someone’s daughter, sons, mothers, fathers, grandparents, uncles, aunties, etc. They all have families and they are fighting at the frontline for YOU. 

Show respect, compassion, and kindness.

Stay home! For yourself, people you care about, and for all the front liners. 

orange and white digital watch
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1. Liu, Y. et al. Preprint at bioRxiv (2020).
2. Ong, S. W. X. et al. J. Am. Med. Assoc. (2020).
3. Santarpia, J. L. et al. Preprint at medRxiv (2020).
4. Van Doremalen, N. et al. N. Engl. J. Med. (2020).
5. Yan, J. et al. Proc. Natl Acad. Sci. USA 115, 1081–1086 (2018).
6. Cheng, V. C. C. et al. Infect. Control Hosp. Epidemiol. (2020).
7. Lewis, D. Is the coronavirus airborne? Experts can’t agree. Nature 580, 175-175 (2020).

About the Author

Ameline Lim, Ph.D.
Ameline Lim, Ph.D., is a research scientist and biologist. She received her PhD from the University of New South Wales at Sydney, Australia. She has broad interests in medicine, history of science, and behavioural science. She is particularly interested in science education and the public understanding of scientific research. Her blog 'Science with Amy' celebrates the pleasures of finding things out and general curiosity.