A Canadian study on flu has clear implications for COVID-19, as it found that an unobstructed cough could travel over two metres (six feet) in less than three seconds, and keep going.
First reported by the South China Morning Post on Thursday, the study was led by Canada's Western University and has been accepted for publication in the journal Indoor Air was done in the 2017-18 flu season - well before the COVID-19 struck.
"Even when you are 2.5 metres away, the airflow in the cough can still be moving at 200mm (eight inches) a second," said Eric Savory, professor from department of mechanical and materials engineering at Western University.
"The very fine droplets are going to remain suspended for a long time, even after four seconds."
According to the World Health Organisation (WHO), the virus is transmitted through respiratory droplets and contact routes.
Another study this month by an MIT researcher claimed that new coronavirus droplets could travel up to 27 feet as a sneeze or a cough results in a turbulent gas cloud that could contain SARS-CoV-2 droplets.
In a paper published in the Journal of the American Medical Association (JAMA), Lydia Bourouiba, associate professor at MIT and an expert in fluid dynamics, has suggested to revise social distancing of six feet (2 metres) to limit the risk of exposure as well as currently used surgical and N95 masks which "are not tested for these potential characteristics of respiratory emissions".
In India, the Health Ministry has asked citizens to ensure physical distancing of minimum 1 metre or three feet.
"Recent work has demonstrated that exhalations, sneezes, and coughs not only consist of mucosalivary droplets following short-range semiballistic emission trajectories but, importantly, are primarily made of a multiphase turbulent gas (a puff) cloud that entrains ambient air and traps and carries within it clusters of droplets with a continuum of droplet sizes," Bourouiba emphasized.
The locally moist and warm atmosphere within the turbulent gas cloud allows the contained droplets to evade evaporation for much longer than occurs with isolated droplets.
"Under these conditions, the lifetime of a droplet could be considerably extended by a factor of up to 1000, from a fraction of a second to minutes," said Bourouiba.
Dr Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, however urged caution with the MIT study during a White House briefing.
"This could really be terribly misleading," he said, adding that it would apply only to people with extremely strong sneezes.
An earlier research by the Centers for Disease Control and Prevention (CDC) revealed that the coronavirus RNA was present even after 17 days on a Diamond Princess cruise ship in Japan.