Scientists are still investigating the origin of the COVID-19 virus which has paralysed huge areas of the planet - but one theory suggests it isn’t as new as we think.
A study recently published in Nature highlighted the fact that the virus is definitely not man-made, and is the product of natural evolution.
But ScienceAlert reports it also suggests a scenario where the virus has been circulating undetected for some time, possibly years.
Latest coronavirus news, updates and advice
The researchers wrote: "It is possible that a progenitor of SARS-CoV-2 jumped into humans,” and acquired new features “during undetected human-to-human transmission”.
"Once acquired, these adaptations would enable the pandemic to take off and produce a sufficiently large cluster of cases to trigger the surveillance system that detected it."
Coronaviruses are zoonotic, meaning they are transmitted between animals and people, the World Health Organisation (WHO) says.
Coronaviruses are a large family of viruses that cause illnesses ranging from the common cold to more severe diseases such as Severe Acute Respiratory Syndrome (Sars).
The researchers suggest that it’s possible the virus could have “jumped” into humans many times, writing: “Sufficient opportunity could have arisen if there had been many prior zoonotic events that produced short chains of human-to-human transmission over an extended period.”
This week, Boris Johnson wrote to 30 million households across the country warning that the outbreak will get “worse before it gets better”.
On Sunday, a key government doctor said normal life will not resume for at least six months as all parts of the UK are placed on an “emergency footing” to tackle the outbreak.
Dr Jenny Harries, deputy chief medical officer for England, said the nation will not be in “complete lockdown” for half a year but that social distancing measures will be lifted gradually.
Meanwhile, the prime minister, who is in isolation in his flat above 11 Downing Street, revealed in a video message that some 20,000 former NHS staff have returned to help in the fight against the outbreak.
He also said the UK will get through the coronavirus crisis “together”.
“We are going to do it, we are going to do it together. One thing I think the coronavirus crisis has already proved is that there really is such a thing as society,” Johnson said.