Around 60 per cent of infectious diseases have animal origins, and bats alone have been responsible for Ebola, Severe Acute Respiratory Syndrome (Sars), rabies and some strains of influenza.
The virus was sequenced in January, and by February was found to share 96 per cent of its genetic code with a coronavirus called RaTG13 that circulates in Chinese bats. In May, scientists got even closer to the source, finding that the virus was 97.1 per cent similar to a disease named RmYN02, found in bats in China’s Yunnan province.
However, because neither virus is the direct ancestor of the new disease, some experts have speculated that it jumped into humans from an intermediary species, possibly a pangolin.
Early conspiracy theories suggested the virus was man-made and may have leaked from a Chinese research laboratory.
A pre-print research article suggested the DNA of the virus contained HIV code, and in April the French biologist and Nobel laureate Luc Montagnier claimed it was a botched attempt to create an AIDS vaccine.
The US Secretary of State, Mike Pompeo, has said there was “enormous evidence” that the virus originated in a lab, and a report in May suggested there may have been an emergency shutdown at the Wuhan Institute of Virology in October after mobile phone activity eased between October 7 and October 24.
British geneticists claim it is currently impossible to genetically edit a virus to look like coronavirus.
Yet the idea that a deadly virus escaped from a lab is not as far-fetched as it sounds. In 2004, the Sars virus escaped from a high-containment research lab in Beijing at least three times, causing local outbreaks.
And it might yet turn out that coronavirus did not start in China at all. In June, Spanish virologists announced that they had found traces of the disease in samples of waste water collected in March last year, nine months before the Covid-19 disease was seen in China.
Italian scientists also found evidence of coronavirus in sewage samples in Milan and Turin in mid-December, many weeks before the first case was detected, while experts found traces in Brazil in November.
What is the current death rate?
The death rate is still very difficult to determine because there are so many cases of asymptomatic coronavirus.
Globally, the overall mortality rate is hovering around 3.9 per cent, based on the number of people who died after testing positive for coronavirus.
However, studies have shown that the number of asymptomatic cases may be 10 times higher than positive tests, which would bring the death rate down to just 0.39 per cent – around four times higher than flu.
That figure may be lower still because asymptomatic testing only takes into account antibody responses. It has been shown that many people – particularly the under-40s – who contract the virus never develop antibodies and use a different part of the immune system to fight the disease.
In Britain, the death rate for those hospitalised with Covid-19 has fallen dramatically since the peak of the epidemic, when six per cent of people were dying. By June, that had dropped to just 1.5 per cent.
There are now several drugs in use or being trialled in the NHS that appear to have an impact on survival, and doctors have generally become better at treating the illness. But the chance of death varies widely, based on age, ethnicity and underlying health conditions (see graphic below).