Half of all coronavirus patients show NO symptoms at all – but are still infectious
AROUND half of all coronavirus patients show no symptoms at all but are still infectious, a new study has revealed.
Scientists say that while the two warning signs of Covid-19 are a dry cough and a temperature - for about 50 per cent of individuals infected, the deadly illness is "invisible".
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It comes amid the growing fears that these infected carriers are slipping under the radar and could be behind the staggering advance of the coronavirus pandemic.
Researchers made the revelation after gathering data from Iceland, the Italian town of Vò, and the Diamond Princess cruise ship.
In these three places even people without symptoms of coronavirus were tested – which is not the case in the UK, where tests are reserved for seriously ill patients in hospital.
And in each of these locations, around half of all individuals with coronavirus were asymptomatic.
On the Diamond Princess cruise ship, of the 3,711 passengers who were tested, 712 tested positive, and 331 (46 percent) didn't show symptoms, according to Japan’s health agency.
Similarly, in the small northern Italian town of Vò, where Italy’s first coronavirus death occurred, the entire population of 3,000 people was tested.
The researchers were surprised to find that “a significant proportion of the population, about 3 per cent, had already been infected – yet most of them were completely asymptomatic.”
And in Iceland, more than six per cent of the entire country has been tested, by far the largest proportion in the world.
Nearly half of those tests have been done as part of a “screening program," in which anyone who asks for a test can get one, even if they have mild or no symptoms.
“Of the 5,502 samples taken in the screening program between March 13-19, 50 tested positive for SARS-CoV-2... 66 per cent of those individuals reported symptoms, such as coughing and body ache,” Kjartan Hreinn Njálsson, at the Icelandic Directorate of Health, told , adding that the other third had no symptoms.
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Njálsson added that non-symptomatic people can spread the disease, but, “we know that the virus is much more likely to spread from person to person if the infected one is showing symptoms."
Experts say the discovery that about half of all coronavirus patients show no symptoms at all has critical implications and shows that even more widespread testing may be needed to identify all carriers.
Patrick T. Dolan, a virologist at University of California, San Francisco said: "Many cases are apparently asymptomatic.
"This is both good and bad news, because it means the virus lethality may be lower than initially thought, but also that people can unknowingly spread the virus.
“It is still too early to be certain of the numbers, but it is clear that asymptomatic infection is contributing significantly to the spread of SARS-CoV2.
"This is exactly why strict adherence to social distancing measures is critical."
A separate report this weekend has also revealed that asymptomatic coronavirus cases appear to be on the rise in China.
that the country’s National Health Commission identified 78 new cases considered asymptomatic in Beijing - whereas there were only 47 the day before.
It comes as Chinese leaders have begun loosening tough travel restrictions following lockdown.
Health officials warned early on in the outbreak of the new infection that it is possible to spread through "hidden webs".
And a string of recent studies indicate people without Covid-19 symptoms are acting as unseen “super spreaders”.
People can “shed” or emit the virus in the incubation period before they show symptoms.
Research published recently found that those infected with Covid-19 can take a staggering five days for coronavirus symptoms to show - and they can still appear after the quarantine period.
The new study, from the Johns Hopkins Bloomberg School of Public Health in the US, found that the average incubation period is 5.1 days.
And they say that almost all - 97.5 per cent - of those who develop symptoms appeared to do so within 11.5 days of infection.
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More on coronavirus
In another study, scientists from the United States, France, China and Hong Kong, found that time between cases in a chain of transmission is less than a week.
Their findings, published in the journal Emerging Infectious Diseases, also showed that more than ten per cent of patients are infected by somebody who has the virus but does not yet have symptoms.
Children are often asymptomatic carriers of Covid-19 and can pose a particular risk to those closest to them.