Scientists Question if 6ft Social Distancing Is Enough to Stop Coronavirus Spread, as Coughs Appear to Spread Saliva 19ft

Scientists fear socially distancing by six feet may not be enough to protect people from saliva droplets which may be carrying germs like the coronavirus which causes COVID-19.

Researchers at the University of Nicosia, Cyprus, used existing data on coughs and saliva to create a computer simulation to predict how it moves through the air in different conditions. When a person coughs or sneezes, droplets of saliva form, and can burst out in moist, warm clouds of gas, the team explained in the study, published in the journal Physics of Fluids. The model took into account factors including wind speed in an open environment, how big the droplets were, the shape of a person's mouth when coughing, as well as the intensity of the cough and how long it lasted. They also considered the temperature of the saliva, the human mouth and external temperature, as well as the relative humidity.

The computer model suggests that saliva droplets can travel up to 6 meters (19 ft) in wind speeds of 4 to 15 km/h (2 mph to 9 mph). The concentration and size of the droplets appeared to reduce in the direction of the wind.

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Wind shown blowing left to right at speeds of 4 kph (top) and 15 kph (bottom) can transport saliva droplets up to 19 ft. Image courtesy of the authors

The way that the saliva seemed to settle suggested that droplet clouds could affect people of different heights in different ways. "Shorter adults and children could be at higher risk if they are located within the trajectory of falling droplets," they wrote.

In addition, the model indicated droplets reduce in size more slowly when the wind speed is lower than at a higher speed. This may mean people are exposed to droplets for longer if they are located near the droplet cloud.

"Our findings imply that depending on the environmental conditions, the 2 meters social distance may not be sufficient," they wrote.

Asked how the research could be used to tackle the COVID-19 pandemic, co-author Professor Dimitris Drikakis of the Science and Engineering and Medical Schools at the University of Nicosia told Newsweek: "In open spaces, airborne droplets can travel significantly further than the 2 m (6 ft) recommended distance depending on the wind speed and the environmental conditions. The above is an important finding, and both citizens and policy-makers should be aware of it."

Drikakis said: "If a person is in the path of the virus cloud, the risk of infection will, most likely, depend on the dosage and time of exposure. Therefore, it is crucial to better understand which scenarios may allow the transmission at longer distances. The present study contributes to advancing the above understanding."

He went on: "Further research is necessary to understand the conditions under which patients are being infected."

That includes more work related to how big droplets are when they are created, and how they evaporate, particularly in different environmental conditions, Drikakis said.

"The violent cough of patients with respiratory diseases will affect droplet generation and secretions of fluids on airway surfaces and heighten coughing frequency. These factors need to be further quantified," he explained. "Moreover, the dosage and time needed for infection are not yet understood and may vary from one person to another."

Dr. Simon Clarke, associate professor in cellular microbiology at the University of Reading who did not work on the paper, said in a statement: "The fact that droplets from a cough can travel for more than 2m (6 ft) is already understood, but this new study helps to provide more insight into the physical mechanisms at work as droplets travel through the air.

"This is a reminder that the 2m (6 ft) rule is recommended, not because staying 2m (6 ft) away from all other people provides you with a force field against infection, but because it is a reasonable distance to stay away from people to reduce risk of infection. While 2m is better than 1m (3ft), 10m (32 ft) or 100m (328 ft) is even better, although the protective effect is not proportional to the distance."

Clarke stressed: "The most important point to take away from this paper is not that we need to change guidelines on social distancing, but that coughing is one of the best ways to spread infected droplets if you're ill. So if you have a cough, stay at home until you're better—and if you cough unexpectedly when you are out and about, cough into your elbow. Then go home, and stay there."

Julian Tang, associate professor of respiratory sciences at the U.K.'s University of Leicester, who did not work on the study, said in a statement the findings "are not that surprising—if the wind is blowing in the right direction then droplets from exhaled breath (whether from breathing, talking, coughing, laughing, singing)—can reach other people.

"But in reality, there will be a lot of dilution in the process, especially being outdoors—so exactly how many droplets carrying how much virus will differ in each scenario."

Tang said: "If the dilution factor is great enough, the actual number of viable viruses reaching someone else may not be enough to cause infection or disease. But it [the study] does show that the 2 m separation rule will not prevent all transmission events—but will likely prevent more than a 1 m separation—or no separation at all.

"Note that the reduction of transmission risk is all incremental—masking, social distancing, lockdown—but it all adds up to reducing the transmission of the virus through the population."

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A graph showing the countries with the most known COVID-19 cases. Statista