FOR thousands of people across the globe, the new coronavirus has triggered life-threatening symptoms.
But for as many as 25 percent of individuals infected with Covid-19 - the deadly illness has been practically invisible.
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The warning signs of coronavirus include a new, continuous cough, a high temperature or shortness of breath.
However, doctors have now revealed that some people with Covid-19 may not show any of these three signs of coronavirus.
And if you don't display any symptoms - known as being 'asymptomatic' - then the risk of infecting others increases.
The US Centers for Disease and Control (CDC) said: "Some spread might be possible before people show symptoms; there have been reports of this occurring with this new coronavirus, but this is not thought to be the main way the virus spreads."
There have been growing fears that these infected carriers are slipping under the radar and could be behind the staggering advance of the disease.
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”.
The CDC has warned that 25 per cent of people infected with the new coronavirus may not show symptoms.
But how long can asymptomatic coronavirus carriers infect others for?
Researchers are currently scrambling to gauge the risk of Covid-19 transmission from people who appear to be healthy.
The exact rate of asymptomatic transmission is unknown, but inferences are it’s very high.
The CDC believes that people who have been infected with Covid-19 are at their most contagious at the peak of their symptoms.
This means that the days people feel their worst ― that may include a cough or a fever ― are when they’re most likely to spread the virus.
But that does not mean it is the only time they are contagious.
People can “shed” or emit the virus in the incubation period before they show symptoms.
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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.
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.
Children are often asymptomatic carriers of Covid-19 and can pose a particular risk to those closest to them.
Dr. Faheem Younus, chief of infectious diseases at the University of Maryland Upper Chesapeake Health, told HuffPost: "The longer the duration, the closer the contact, the lower the host’s immunity, the higher the risk of catching the infection."
In general, individuals who are suspected of having Covid-19 are asked to remain in isolation for at least three days after they have recovered and for at least a week after their symptoms first appeared.
Experts say we should all act like we’re already a carrier of the virus and follow current recommendations for preventing transmission.
In particular, health bosses say the best way to protect yourself is to wash your hands with soap and water for the time it takes to sing Happy Birthday twice.
Happy Birthday takes about 20 seconds to sing twice and is said to be the perfect number to clean your hands to thoroughly.
You should also not touch your eyes, nose or mouth with unwashed hands and avoid close contact with people who are sick.
Cleaning and disinfecting objects and surfaces which you may have touched is also important.
The Government are also urging people to stay at home and only go outside for food, health reasons or work - but only if you cannot work from home.
If you go out, stay two metres away from other people at all times and wash your hands as soon as you get home.