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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, 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.

Washington, May 27: Most viruses and other germs do not spread easily on flights, the US Center for Disease Control and Prevention has said in its COVID-19 guidelines which do not recommend following social distancing between two passengers inside a plane or keeping the middle seat unoccupied.

As a result of coronavirus pandemic, air traffic inside the US has come to a near halt. Air traffic is said to be down to about 90 per cent. For all travellers coming from overseas, the Center for Disease Control and Prevention (CDC) has recommended 14 days quarantine.

"Most viruses and other germs do not spread easily on flights because of how air circulates and is filtered on aeroplanes," the CDC has said in its set of COVID-19 guidelines for air travellers.

However, it noted that the air travellers were not risk-free especially in the time of the coronavirus pandemic and recommended Americans to avoid travel as far as possible.

"Air travel requires spending time in security lines and airport terminals, which can bring you in close contact with other people and frequently touched surfaces," it said.

"Social distancing is difficult on crowded flights, and you may have to sit near others (within six feet), sometimes for hours. This may increase your risk for exposure to the virus that causes COVID-19," the CDC said.

But instead of recommended social distancing inside commercial planes, the CDC has advised a series of preventive and hygienic measures to be taken by the airlines pilot and crew to prevent the spread of coronavirus.

The US Department of Transportation and Federal Aviation Administration in its latest safety alerts for operators on May 11 said that air carriers and crews conducting flight operations having a nexus to the US, including both domestic and foreign air carriers, should follow CDC's occupational health and safety guidance.

The CDC issued its guidelines in first guidelines for the airlines and airline crew on March and again in May.

The CDC, which has issued an exhaustive social guideline measures in various sections, is silent on keeping the middle seat of a plane unoccupied so as to maintain the six feet distance between two passengers.

It calls for the plane crew to report to the CDC a traveller with specific COVID-19 symptoms like fever, persistent cough, difficulty in breathing and appearing unwell.

Asking the airlines and cabin crew to review infection control guidelines for cabin crew, the CDC recommends several measures for cabin crew to protect themselves and others, manage a sick traveller, clean contaminated areas, and take actions after a flight.

Prominent among them include washing hands often with soap and water for at least 20 seconds, particularly after assisting sick travellers or touching potentially contaminated body fluids or surfaces and use of alcohol-based hand sanitizer (containing at least 60 per cent alcohol) if soap and water are not available.

Airlines should consider providing alcohol-based hand sanitizer to cabin and flight crews for their personal use, it said.

The CDC guidelines do not recommend following social distancing inside a plane between two passengers or keeping the middle seat unoccupied. But it asks to minimise contact between passengers and cabin crew and the sick person.

"If possible, separate the sick person from others (by a distance of 2 meters or 6 feet, ideally) and designate one crew member to serve the sick person. Offer a facemask, if available and if the sick person can tolerate it. If a facemask is not available or cannot be tolerated, ask the sick person to cover their mouth and nose with tissues when coughing or sneezing," said the CDC guidelines.

If no symptomatic passengers were identified during or immediately after the flight, the CDC recommends airlines to follow routine operating procedures for cleaning aircraft, managing solid waste, and wearing PPE.

"If symptomatic passengers are identified during or immediately after the flight, routine cleaning procedures should be followed, and enhanced cleaning procedures should also be used," it said.

Clean porous (soft) surfaces (e.g, cloth seats, cloth seat belts) at the seat of the symptomatic passengers and within 6 feet of the symptomatic passengers in all directions, it added.