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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.

Melbourne, July 1: Authorities will lock down around 300,000 people in suburbs north of Melbourne for a month from late on Wednesday to contain the risk of infection after two weeks of double-digit rises in new coronavirus cases in Australia's second-most populous state.

Australia has fared better than many countries in the pandemic, with around 7,830 cases and 104 deaths, but the recent surge has stoked fears of a second wave of COVID-19, echoing concerns expressed in other countries.

Globally, coronavirus cases exceeded 10 million on Sunday, a major milestone in the spread of a disease that has killed more than half a million people in seven months.

From midnight, more than 30 suburbs in Australia's second-biggest city will return to stage three restrictions, the third-strictest level in curbs to control the pandemic. That means residents will be confined to home except for grocery shopping, health appointments, work or caregiving, and exercise.

The restrictions will be accompanied by a testing blitz that authorities hope will extend to half the population of the area affected, and for which borders will be patrolled, authorities said. The measures come as curbs ease across the rest of the state of Victoria, with restaurants, gyms and cinemas reopening in recent weeks.

Victoria recorded 73 fresh cases on Tuesday from 20,682 tests, following an increase of 75 cases on Monday. State premier Daniel Andrews warned on Wednesday that the return of broader restrictions across city remained a possibility.

"If we all stick together these next four weeks, we can regain control of that community transmission ... across metropolitan Melbourne," Andrews said at a briefing. "Ultimately if I didn't shut down those postcodes I'd be shutting down all postcodes. We want to avoid that."

Victoria's spike in cases has been linked to staff members at hotels housing returned travellers for which quarantine protocols were not strictly followed. Victorian state authorities have announced an investigation into the matter.

Some other Australian states and territories are preparing to open borders, but applying limits and quarantine measures to citizens of Victoria as the school holiday season gets under way.

South Australia, the country's fifth most populous state, has had just three new cases in the past month. But citing the spike in coronavirus infections, on Tuesday it cancelled its scheduled reopening to other parts of the nation.

New South Wales (NSW), Australia's most populous state, has stopped short of closing its borders to all Victorians, but those holidaying from hotspot areas - not permitted under NSW rules - can be handed a fine of A$11,000 ($7,596) or jailed if they are detected, state authorities said.

The delays reopening internal borders cast doubts over a federal plan to set up "travel bubble" with neighbouring New Zealand that would allow movement between the two countries.

Beijing, Mar 25: Around 5,000 people have signed up for the phase I clinical trial of recombinant novel coronavirus vaccine in Chinese city Wuhan where the virus first emerged late last year.

The recruitment for participants ended this week with nearly 5,000 volunteers signing up for the trial, state-run Beijing News reported on Wednesday.

A single-centre, open and dose-escalation phase I clinical trial for recombinant novel coronavirus vaccine (adenoviral vector) will be tested in healthy adults aged between 18 and 60 years, according to the ChiCTR (China Clinical Trial Register).

The trial, led by experts from the Academy of Military Medical Sciences, gained its approval on March 16 and the research is expected to last half a year.

Requiring at least 108 participants, the trial will be conducted in Wuhan, capital of Hubei province, the region worst-affected by the virus in the country, state-run China Daily reported.

Participants will experience 14-day quarantine restrictions after being vaccinated and their health condition will be recorded every day.

Chinese scientists are hastening the development of COVID-19 vaccines through five approaches --- inactivated vaccines, genetic engineering subunit vaccines, adenovirus vector vaccines, nucleic acid vaccines and vaccines using attenuated influenza virus as vectors.

So far, most teams are expected to complete preclinical research in April and some are moving forward faster, Wang Junzhi, an academician with the Chinese Academy of Engineering said.

Wang noted that research and development of COVID-19 vaccines in China is not slower than foreign counterparts and has been carried out in a scientific, standardised and orderly way.

China has stepped up the process to finalise vaccines to counter COVID-19 after Kaiser Permanente research facility in Seattle and Washington stole the march and began human trials.

China lifted tough restrictions on the Hubei province on Wednesday after a months-long lockdown as the country reported no new domestic cases.

But there were another 47 imported infections from overseas, the National Health Commission said. In total, 474 imported infections have been diagnosed in China -- mostly Chinese nationals returning home.