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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.

Houston, Mar 15: Researchers, studying the novel coronavirus, have found that the time between cases in a chain of transmission is less than a week, and over 10 per cent of patients are infected by someone who has the virus, but does not show symptoms yet, a finding that may help public health officials contain the pandemic.

The study, published in the journal Emerging Infectious Diseases, estimated what's called the serial interval of the coronavirus by measuring the time it takes for symptoms to appear in two people with the virus -- the person who infects another, and the infected second person.

According to the researchers, including those from the University of Texas at Austin, the average serial interval for the novel coronavirus in China was approximately four days.

They said the speed of an epidemic depends on two things -- how many people each case infects, and how long it takes cases to spread.

The first quantity, the scientists said, is called the reproduction number, and the second is the serial interval.

Due to the short serial interval of the disease caused by the coronavirus -- COVID-19 -- they said, emerging outbreaks will grow quickly, and could be difficult to stop.

“Ebola, with a serial interval of several weeks, is much easier to contain than influenza, with a serial interval of only a few days,” said Lauren Ancel Meyers, study co-author from UT Austin.

Meyers explained that public health responders to Ebola outbreaks have much more time to identify and isolate cases before they infect others.

“The data suggest that this coronavirus may spread like the flu. That means we need to move quickly and aggressively to curb the emerging threat,” Meyers added.

In the study, the scientists examined more than 450 infection case reports from 93 cities in China, and found the strongest evidence yet that people without symptoms must be transmitting the virus -- known as pre-symptomatic transmission.

More than one in ten infections were from people who had the virus but did not yet feel sick, the scientists said.

While researchers across the globe had some uncertainty until now about asymptomatic transmission with the coronavirus, the new evidence could provide guidance to public health officials on how to contain the spread of the disease.

“This provides evidence that extensive control measures including isolation, quarantine, school closures, travel restrictions and cancellation of mass gatherings may be warranted,” Meyers said.

The researchers cautioned that asymptomatic transmission makes containment more difficult.

With hundreds of new cases emerging around the world every day, the scientists said, the data may offer a different picture over time.

They said infection case reports are based on people's memories of where they went and whom they had contact with, and if health officials move quickly to isolate patients, that may also skew the data.

“Our findings are corroborated by instances of silent transmission and rising case counts in hundreds of cities worldwide. This tells us that COVID-19 outbreaks can be elusive and require extreme measures,” Meyers said.

London, May 12: British Prime Minister Boris Johnson has warned that a mass vaccine for the novel coronavirus may be over a year away and, in the worst-case scenario, may in fact never be found.

In his foreword to the government’s new 50-page guidance on a step by step easing of the lockdown measures in place to control the spread of the deadly virus, the UK prime minister lays out plans for businesses to gradually start reopening with “COVID-19 Secure” measures of social distancing and for the public to use “good solid British common sense” as the economy is unlocked.

“A mass vaccine or treatment may be more than a year away,” said Johnson, highlighting the work being done in the UK by scientists at Oxford University and Imperial College London towards this mission.

“Indeed, in a worst-case scenario, we may never find a vaccine. So our plan must countenance a situation where we are in this, together, for the long haul, even while doing all we can to avoid that outcome,” he said.

Admitting that a vaccine or drug-based treatment is the only “feasible long-term solution”, he said the UK has accelerated this with “promising” vaccine development programmes and a collaboration between Oxford University and pharma major AstraZeneca was a vital step that could help rapidly advance the manufacture of a Covid-19 vaccine when it is ready.

As part of global efforts, he flagged the GBP 388 million in aid funding for research into vaccines, tests and treatment, including GBP 250m to the Coalition for Epidemic Preparedness Innovations.

“But while we hope for a breakthrough, hope is not a plan,” he said, as he unveiled his plan for starting to lift lockdown restrictions from this week in phases.

Following a televised address to the nation on Sunday night and a statement in Parliament on Monday, the guidance comes into effect in public life across England from Wednesday when people will be allowed one-to-one contact with people other than those they live with, as long as they remain outside and two metres apart.

They are allowed to play sport with a friend or family member from outside their household or socialise with them in the open air for the first time in more than six weeks since the lockdown was imposed.

People are still advised to work from home where possible but start heading into work where necessary, in sectors such as construction and manufacturing, keeping the social distancing norms in place.

Under the step by step plan, by the start of next month non-essential shops will also reopen, with some hairdressers, pubs and cinemas to follow from July. However, as part of a Covid-19 Alert System, if infection rates are seen to be rising again, restrictions would be tightened “possibly at short notice”.

Fines for breaching the new rules will also be increased to GBP 100 and will double for each repeat offence, up to a maximum of GBP 3,200.

Johnson said: "I must ask the country to be patient with a continued disruption to our normal way of life, but to be relentless in pursuing our mission to build the systems we need. The worst possible outcome would be a return to the virus being out of control – with the cost to human life, and – through the inevitable re-imposition of severe restrictions – the cost to the economy. We must stay alert, control the virus, and in doing so, save lives.

“Then, as vaccines and treatment become available, we will move to another new phase, where we will learn to live with Covid-19 for the longer term without it dominating our lives.”

The devolved administrations of Scotland and Wales are putting their own measures in place and keeping the “stay at home” message in place, rather than switch to the new “stay alert” message.

The UK government’s latest messaging has come under attack from the Opposition and other sections of society over a feared lack of clarity for the general public.