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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.

May 18: Risk managers expect a prolonged global recession as a result of the coronavirus pandemic, a report by the World Economic Forum showed on Tuesday.

Two-thirds of the 347 respondents to the survey - carried out in response to the outbreak - put a lengthy contraction in the global economy top of their list of concerns for the next 18 months.

Half of risk managers expected bankruptcies and industry consolidation, the failure of industries to recover and high levels of unemployment, particularly among the young.

“The crisis has devastated lives and livelihoods. It has triggered an economic crisis with far-reaching implications and revealed the inadequacies of the past," said Saadia Zahidi, managing director of the World Economic Forum.

Environmental goals risk being discarded as a result of the pandemic, the report said, but governments should try to carve out a "green recovery".

"We now have a unique opportunity to use this crisis to do things differently and build back better economies that are more sustainable, resilient and inclusive," Zahidi said.

The report was compiled by the World Economic Forum’s Global Risks Advisory Board together with Marsh & McLennan Companies Inc and Zurich Insurance Group.

Risk managers were surveyed between April 1 and 13.

Six months since the new coronavirus outbreak, the pandemic is still far from over, the World Health Organization said Monday, warning that "the worst is yet to come".

Reaching the half-year milestone just as the death toll surpassed 500,000 and the number of confirmed infections topped 10 million, the WHO said it was a moment to recommit to the fight to save lives.

"Six months ago, none of us could have imagined how our world -- and our lives -- would be thrown into turmoil by this new virus," WHO chief Tedros Adhanom Ghebreyesus told a virtual briefing.

"We all want this to be over. We all want to get on with our lives. But the hard reality is this is not even close to being over.

"Although many countries have made some progress, globally the pandemic is actually speeding up.

"We're all in this together, and we're all in this for the long haul.

"We will need even greater stores of resilience, patience, humility and generosity in the months ahead.

"We have already lost so much -- but we cannot lose hope."

Tedros also said that the pandemic had brought out the best and worst humanity, citing acts of kindness and solidarity, but also misinformation and the politicisation of the virus.

In an atmosphere of global political division and fractures on a national level, "the worst is yet to come. I'm sorry to say that," he said.

"With this kind of environment and condition, we fear the worst."