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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.

UN, May 26: Countries could see a "second peak" of coronavirus cases during the first wave of the pandemic if lockdown restrictions were lifted too soon, the World Health Organization (WHO) has warned.

Mike Ryan, the WHO's head of emergencies, told a briefing on Monday that the world was "right in the middle of the first wave", the BBC reported.

He said because the disease was "still on the way up", countries need to be aware that "the disease can jump up at any time".

"We cannot make assumptions that just because the disease is on the way down now that it's going to keep going down," Ryan said.

There would be a number of months to prepare for a second peak, he added.

The stark warning comes as countries around the world start to gradually ease lockdown restrictions, allowing shops to reopen and larger groups of people to gather.

Experts have said that without a vaccine to give people immunity, infections could increase again when social-distancing measures are relaxed.

Ryan said countries where cases are declining should be using this time to develop effective trace-and-test regimes to "ensure that we continue on a downwards trajectory and we don't have an immediate second peak".

Also on Monday, Tedros Adhanom Ghebreyesus, WHO Director-General, said that a clinical trial of hydroxychloroquine (HCQ) on COVID-19 patients has come to "a temporary pause", while the safety data of the the anti-malaria drug was being reviewed.

According to the WHO chief, The Lancet medical journal on May 22 had published an observational study on HCQ and chloroquine and its effects on COVID-19 patients that have been hospitalized, reports Xinhua news agency.

The authors of the study reported that among patients receiving the drug, when used alone or with a macrolide, they estimated a higher mortality rate.

"The Executive Group of the Solidarity Trial, representing 10 of the participating countries, met on Saturday (May 23) and has agreed to review a comprehensive analysis and critical appraisal of all evidence available globally," Tedros said in a virtual press conference.

The developments come as the total number of global COVID-19 cases has increased to 5,508,904, with 346,508 deaths, according to the Johns Hopkins University.

Washington, Apr 2: The total US death toll from the coronavirus pandemic topped 4,000 early Wednesday, more than double the number from three days earlier, according to a tally by Johns Hopkins University.

The number of deaths was 4,076 -- more than twice the 2,010 recorded late Saturday.

More than 40 percent of recorded deaths nationally were in New York state, the Johns Hopkins data showed.

On Tuesday the United States exceeded the number of deaths in China, where the pandemic emerged in December before spreading worldwide.

The number of confirmed US cases has reached 189,510, the most in the world, though Italy and Spain have recorded more fatalities.

After initially downplaying the threat from new coronavirus in the early stages of the US outbreak, President Donald Trump warned of "a very, very painful two weeks" to come for the country on Tuesday.