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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.

Beijing:  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.

Berlin, Mar 28: The number of confirmed coronavirus infections worldwide topped 600,000 on Saturday as new cases stacked up quickly in Europe and the United States and officials dug in for a long fight against the pandemic.

The latest landmark came only two days after the world passed half a million infections, according to a tally by John Hopkins University, showing that much work remains to be done to slow the spread of the virus. It showed more than 602,000 cases and a total of over 27,000 deaths.

While the U.S. now leads the world in reported infections — with more than 104,000 cases — five countries exceed its roughly 1,700 deaths: Italy, Spain, China, Iran and France.

“We cannot completely prevent infections at this stage, but we can and must in the immediate future achieve fewer new infections per day, a slower spread,” German Chancellor Angela Merkel, who is in quarantine at home after her doctor tested positive for the virus, told her compatriots in an audio message. “That will decide whether our health system can stand up to the virus.”

The virus already has put health systems in Italy, Spain and France under extreme strain. Lockdowns of varying severity have been introduced across Europe. Merkel's chief of staff, Helge Braun, said that Germany — where authorities closed nonessential shops and banned gatherings of more than two in public — won't relax its restrictions before April 20.

As the epicenter has shifted westward, the situation has calmed in China, where some restrictions on people's lives have now been lifted. Six subway lines restored limited service in Wuhan, where the virus first emerged in December, after the city had its official coronavirus risk evaluation downgraded from high to medium on Friday. Five districts of the city of 11 million people had other restrictions on travel loosened after their risk factor was downgraded to low.

For most people, the coronavirus causes mild or moderate symptoms, such as fever and cough that clear up in two to three weeks. But for others, especially older adults and people with existing health problems, the virus can cause more severe illness, including pneumonia, and lead to death.

More than 130,000 people have recovered, according to Johns Hopkins' tally.

In one way or another, the effects of the COVID-19 outbreak have been felt by the powerful and the poor alike.

On Friday, British Prime Minister Boris Johnson became the first leader of a major country to test positive for the virus. He said he would continue to work from self-quarantine.

Countries are still scrambling bring home some citizens stranded abroad by border closures and a near-shutdown of flights. On Saturday, 174 foreign tourists and four Nepali nationals on the foothills of Mount Everest were flown out days after being stranded on the only airstrip serving the world's highest mountain.

In neighboring India, authorities sent a fleet of buses to the outskirts of the capital to meet an exodus of migrant workers desperately trying to reach their home villages during the world's largest lockdown.

Thousands of people, mostly young male day laborers but also families, had fled their New Delhi homes after Prime Minister Narendra Modi announced a 21-day lockdown that began on Wednesday and effectively put millions of Indians who live off daily earnings out of work.

In a possibly hopeful sign, the U.S. Food and Drug Administration cleared a new rapid test from Abbott Laboratories, which the company says can detect the coronavirus in about 5 minutes. Medical device maker Abbott announced the emergency clearance of its cartridge-based test Friday night, saying the test delivers a negative result in 13 minutes when the virus is not detected.

While New York remained the worst-hit city in the U.S., Americans braced for worsening conditions elsewhere, with worrisome infection numbers being reported in New Orleans, Chicago and Detroit.

New Orleans’ sprawling Ernest N. Morial Convention Center, along the Mississippi River, was being converted into a massive hospital as officials prepared for thousands more patients than they could accommodate.

In New York, where there are more than 44,000 cases statewide, the number of people hospitalized with COVID-19 passed 6,000 on Friday, double what it had been three days earlier.

Gov. Andrew Cuomo called for 4,000 more temporary beds across New York City, where the Jacob K. Javits Convention Center has already been converted into a hospital.

The struggle to defeat the virus will take “weeks and weeks and weeks,” Cuomo told members of the National Guard working at the Javits Center.

President Donald Trump invoked the Defense Production Act on Friday, ordering General Motors to begin manufacturing ventilators. Trump had previously rejected Cuomo's pleas for tens of thousands more of the machines and the governor's calls to implement the Korean War-era production law.

Trump signed a $2.2 trillion stimulus package, after the House approved the sweeping measure by voice vote. Lawmakers in both parties lined up behind the law to send checks to millions of Americans, boost unemployment benefits, help businesses and toss a life preserver to an overwhelmed health care system.

Dr. John Brooks of the U.S. Centers for Disease Control and Prevention warned Americans remained “in the acceleration phase” of the pandemic and that all corners of the country were at risk.

"There is no geographic part of the United States that is spared from this," he said.