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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.

Canadian researchers are developing a DNA vaccine for SARS-CoV-2, the coronavirus that causes COVID-19 and has currently infected nearly 5,00,000 people worldwide and crippled the global economy.

Entos Pharmaceuticals, a health-care biotechnology company headed by a University of Alberta researchers, develop new therapeutic compounds using the company's proprietary drug-delivery platform and has begun manufacturing vaccine candidates against the novel coronavirus.

"Given the urgency of the situation, we can have a lead candidate vaccine within two months. Once we have that it's a race to get it into clinical trials," said John Lewis, CEO of Entos and a Professor at the University of Alberta in Canada.

Lewis said in comparison to a traditional vaccine, DNA-based vaccines hold several advantages.

Nucleic acids are introduced directly into the patient's own cells, causing them to make pieces of the virus--tricking the immune system into mounting a response without the full virus actually being present, the researcher said.

According to the company, the approach is recognised as being easier to move into large-scale manufacturing, offers improved vaccine stability and works without needing an infectious agent.

In the current absence of a vaccine for COVID-19, several companies around the world are mounting efforts to begin similar work.

The first clinical trial using a DNA-based vaccine developed by Moderna Inc.in the US on March 13.

Their approach allows for antibodies to be made in the human trial volunteers against a specific protein on the surface of the coronavirus that lets the virus enter human cells.

The hope is that the antibodies will stop the interaction.

Though this approach is designed to be effective against COVID-19 specifically, Lewis said Entos is taking a different tack.

The company plans to use plasmid DNA to amplify the production of key coronavirus surface and structural proteins with each injection, with an eye to the bigger picture.

"Many of the structural proteins in the virus are pretty well conserved across all the coronaviruses, including SARS and MERS," said Lewis.

"We're hoping that if we express more of the structural proteins that are common to most coronaviruses, we can inhibit the current COVID-19, and also potentially protect against all coronaviruses both past and future," Lewis added.

To move the project forward quickly, the company is seeking financial support from both provincial and federal levels of government.

"We have the opportunity to save a lot of lives, and I think it's really upon us and governments to find solutions for that," Lewis said.