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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.

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."

Manila, Mar 16: The Philippines has detected an outbreak of avian flu in a northern province after tests showed presence of the highly infectious H5N6 subtype of the influenza A virus in a quail farm, the country's farm minister said on Monday.

Agriculture Secretary William Dar said the bird flu virus, the same strain that hit some local poultry farms in 2017, was detected in Jaen municipality in Nueva Ecija province, where about 1,500 quails had died on one farm alone.

A total of 12,000 quails have been destroyed and buried to prevent further infections, Dar said, citing field reports.

"We are on top of the situation," he said. "Surveillance around the 1-km and 7-km radius will be carried out immediately to ensure that the disease has not progressed around the said perimeter."

Animal quarantine checkpoints have also been set up to restrict the movement of all live domestic birds to and from the quarantine area, he said.

"We would like to emphasise that this is a single case affecting one quail farm only," Dar said.

Dr. Arlene Vytiaco, technical spokeswoman for avian flu at the agriculture department, said that while there is a possibility of transmission to humans through excretion and secretion, "the chances are very slim".

"There is also zero mortality rate," she said.

Dar said his department and the local government were jointly conducting an investigation and contact-tracing to determine the source of infection.

To ensure steady domestic supply of poultry, he said the transport of day-old chicks, hatching eggs and chicken meat will be allowed provided the source farms have tested negative for bird flu.