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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.

Jun 2: Pakistan's COVID-19 cases reached 76,398 on Tuesday after 3,938 new infections were reported across the country, while the death toll due to the coronavirus has gone up to 1,621, according to the health ministry.

The Ministry of National Health Services said that 78 COVID-19 deaths were recorded in the last 24 hours, taking the total number of fatalities in Pakistan to 1,621.

A total of 27, 110 people have recovered, it said.

Sindh has 29,647 patients, Punjab 27,850, Khyber-Pakhtunkhwa 10,485, Balochistan 4,514, Islamabad 2,893, Gilgit-Baltistan 738 and Pakistan-occupied Kashmir 271, it added.

The authorities have conducted 577,974 tests, including 16,548 in the last 24 hours.

The jump in the number of cases comes a day after Prime Minister Imran Khan said that people should learn to live with COVID-19 until a vaccine is developed.

Khan addressed the media after chairing the meeting of National Coordination Committee, the highest body to tackle the pandemic.

"Coronavirus will not go away until the vaccine is discovered. We need to learn to live with it and we can live with it if we follow precautions," he said.

He said the one million volunteers of the government's coronavirus force will raise awareness of the need to follow guidelines.

The government also said that all sectors will be opened slowly after deciding the negative list of businesses which will not be allowed.

Islamabad, Jun 10: The World Health Organization has told Pakistan it should implement "intermittent" lockdowns to counter a surge in coronavirus infections that has come as the country loosens restrictions, officials said.

Since the start of Pakistan's outbreak in March, Prime Minister Imran Khan opposed a nationwide lockdown of the sort seen elsewhere, arguing the impoverished country could not afford it.

Instead, Pakistan's four provinces ordered a patchwork of closures, but last week Khan said most of these restrictions would be lifted.

Health officials on Wednesday declared a record number of new cases in the past 24 hours. The country has now confirmed a total of more than 113,000 cases and 2,200 deaths -- though with testing still limited, real rates are thought to be much higher.

"As of today, Pakistan does not meet any of the pre-requisite conditions for opening the lockdown", the WHO said in a letter confirmed by Pakistan officials on Tuesday.

Many people have not adopted behavioural changes such as social distancing and frequent hand-washing, meaning "difficult" decisions will be required including "intermittent lockdowns" in targeted areas, the letter states.

Some 25 percent of tests in Pakistan come back positive for COVID-19, the WHO said, indicating high levels of infection in the general population.

The health body recommended an intermittent lockdown cycle of two weeks on, two weeks off.

Responding to the WHO's letter, Zafar Mirza, the prime minister's special advisor for health, said the country had "consciously but gradually" eased lockdowns while enforcing guidelines in shops, mosques and public transport.

"We have to make tough policy choices to strike a balance between lives and livelihoods," Mirza said Wednesday.

Punjab's provincial health minister Yasmin Rashid, who received the WHO's letter, said the provincial government had already given "orders to take strict action against those violating" virus guidelines.

Hospitals across Pakistan say they are at or near capacity, and some are turning COVID-19 patients away.

WHO Director-General Tedros Adhanom Ghebreyesus said Monday that 136,000 cases had been reported in the previous 24 hours, "the most in a single day so far", with the majority of them in South Asia and the Americas.