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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.

Scientists predict the world may have a COVID-19 vaccine within one year or even a few months earlier, said the Director-General of the World Health Organisation even as he underlined the importance of global cooperation to develop, manufacture and distribute vaccines.

However, making the vaccine available and distributing it to all will be a challenge and requires political will, Tedros Adhanom Ghebreyesus said on Thursday during a meeting with the European Parliament's Committee for Environment, Public Health and Food Safety.

One option would be to give the vaccine only to those that are most vulnerable to the virus.

There are currently over 100 COVID-19 vaccine candidates in various stages of development.

Adhanom Ghebreyesus said the pandemic has highlighted the importance of global solidarity and that health should not be seen as a cost but an investment.

He added that all countries in the world must strengthen primary health care and crisis preparedness and stressed the need for EU leadership globally.

While the Director-General said the situation in the EU has improved significantly, he underlined that COVID-19 is very much still circulating globally, with more than four million new cases in the last month.

Many Members of European Parliament said that the global community must cooperate including in developing, manufacturing and distributing vaccines against COVID-19 and asked when a safe vaccine could be available.

Several Members of European Parliament underlined the importance of the WHO but also said it has made mistakes in its response to the pandemic.

The Director-General admitted everyone makes mistakes and informed the members that an independent panel will evaluate the WHO response to the pandemic to learn from any mistakes made.

It will start its work soon, he said.

Beijing, May 25: China has reported 51 new coronavirus cases including 40 asymptomatic infections, majority of them in the contagion's first epicentre Wuhan, where over six million tests have been conducted in the last 10 days, health officials said on Monday.

The country's National Health Commission (NHC) said that 11 new imported cases were reported on Sunday.

While no new domestically-transmitted COVID-19 cases were reported in China on Sunday, 11 imported cases including 10 in the Inner Mongolia Autonomous Region and one in Sichuan province were reported, the NHC said in its daily report.

Out of the 40 new asymptomatic cases, 38 were reported in Wuhan, which is currently undergoing mass testing of its over 11.2 million people after a spike in the asymptomatic cases.

Currently, 396 people with asymptomatic symptoms are under medical observation in China, including 326 in Wuhan, according to the health authority.

Asymptomatic cases refer to the patients who have tested COVID-19 positive but develop no symptoms such as fever, cough or sore throat. However, they pose a risk of spreading the disease to others.

Wuhan, which earlier had over 50,000 cases between January and March, started a campaign on May 14 to expand the nucleic acid testing in order to better know the number of asymptomatic cases or people who show no clear symptoms despite carrying the virus.

According to the latest figures released by the Wuhan municipal health commission, the city conducted more than 6 million nucleic acid tests between May 14 and 23.

On Saturday, the city carried out nearly 1.15 million tests, state-run Xinhua news agency reported on Monday.

Nucleic acid testing is a molecular technique for screening blood donations to reduce the risk of transfusion transmitted infections.

As of Sunday, a total of 82,985 confirmed COVID-19 cases have been reported in China with 4,634 fatalities, the NHC added.