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London, May 20: The current physical distancing guidelines of 6 feet may be insufficient to prevent COVID-19 transmission, according to a study which says a mild cough in low wind speeds can propel saliva droplets by as much as 18 feet.

Researchers, including those from the University of Nicosia in Cyprus, said a good baseline for studying the airborne transmission of viruses, like the one behind the COVID-19 pandemic, is a deeper understanding of how particles travel through the air when people cough.

In the study, published in the journal Physics of Fluids, they said even with a slight breeze of about four kilometres per hour (kph), saliva travels 18 feet in 5 seconds.

"The droplet cloud will affect both adults and children of different heights," said study co-author Dimitris Drikakis from the University of Nicosia.

According to the scientists, shorter adults and children could be at higher risk if they are located within the trajectory of the saliva droplets.

They said saliva is a complex fluid, which travels suspended in a bulk of surrounding air released by a cough, adding that many factors affect how saliva droplets travel in the air.

These factors, the study noted, include the size and number of droplets, how they interact with one another and the surrounding air as they disperse and evaporate, how heat and mass are transferred, and the humidity and temperature of the surrounding air.

In the study, the scientists created a computer simulation to examine the state of every saliva droplet moving through the air in front of a coughing person.

The model considered the effects of humidity, dispersion force, interactions of molecules of saliva and air, and how the droplets change from liquid to vapour and evaporate, along with a grid representing the space in front of a coughing person.

Each grid, the scientists said, holds information about variables like pressure, fluid velocity, temperature, droplet mass, and droplet position.

The study analysed the fates of nearly 1,008 simulated saliva droplets, and solved as many as 3.7 million equations.

"The purpose of the mathematical modelling and simulation is to take into account all the real coupling or interaction mechanisms that may take place between the main bulk fluid flow and the saliva droplets, and between the saliva droplets themselves," explained Talib Dbouk, another co-author of the study.

However, the researchers added that further studies are needed to determine the effect of ground surface temperature on the behaviour of saliva in air.

They also believe that indoor environments, especially ones with air conditioning, may significantly affect the particle movement through air.

This work is important since it concerns safety distance guidelines, and advances the understanding of the transmission of airborne diseases, Drikakis said.

Global health experts on Wednesday said novel coronavirus is here to stay for more than a year and called for aggressive testing to prevent its spread.

In an interaction with Congress leader Rahul Gandhi, health experts Professor Ashish Jha and Professor Johan Giesecke talked about the COVID-19 pandemic as part of the series being aired on Congress social media channels.

While Jha exuded confidence that a vaccine will be available in a year's time, Prof Giesecke said India should practice a lockdown that is as 'soft' as possible, as a severe lockdown will ruin its economy very quickly.

"When the economy is opened up after lockdown, you have to create confidence among people," Harvard health expert Ashish Jha told Gandhi.

Jha is a professor of Global Health at TH Chan School of Public Health and Director, Harvard Global Health institute.

He said coronavirus is a '12-18 months' problem and the world is not going to be free of this till 2021.

The expert also called for the need for aggressive testing strategy for high-risk areas.

Gandhi, while interacting with the experts, said life is going to change post COVID-19.

"If 9/11 was a new chapter, this will be a new book," he remarked.

Professor Johan Giesecke, former chief scientist, European Centre for Disease Prevention and Control said India should have a 'soft lockdown'.

"The situation that India is in, I think, you should have a soft lockdown, as soft as possible," he said.

"I think for India, you will ruin your economy very quickly if you have a severe lockdown. It is better, skip the lockdown, take care of the old and the frail...," he noted.