SINGAPORE - As the world enters its third month of grappling with the fast-spreading coronavirus, one question that has dogged governments and medical practitioners is exactly how dangerous the new disease is.

The World Health Organisation (WHO) this week put the Covid-19 global death rate at about 3.4 per cent - far higher than the seasonal flu's 0.1 per cent - but US President Donald Trump has cast doubt on its accuracy.

"Well, I think the 3.4 per cent is really a false number," Mr Trump was quoted by The New York Times as saying on Wednesday (March 4).

"Now, this is just my hunch, and - but based on a lot of conversations with a lot of people that do this ... it's very mild," he said "So, if we have thousands or hundreds of thousands of people that get better just by, you know, sitting around and even going to work - some of them go to work, but they get better."

There may be merit to Mr Trump's comments.

The WHO's ballpark figure reflects a simple calculation based on the number of deaths and confirmed cases. It does not account for mild, undetected cases. It is also mostly derived from the experience in China's Wuhan, the first epicentre of the outbreak, where infections soared before doctors managed to gather the knowledge and resources to battle it.

"Within the rest of China, the mortality rate is in fact much lower," Associate Professor Kenneth Mak, director of medical services at Singapore's Ministry of Health, told reporters at a press conference on Friday (March 6). "And perhaps that is a more accurate figure."

WHO has since clarified that the figure is a broad "snapshot" that will change as the outbreak evolves.

'An over-estimate'

Experts expect the death rate to drop considerably when more information is made known about the illness.

The 3.4 per cent mortality figure "is certainly an overestimate", according to Mr Tom Frieden, a former director of the US Centres for Disease Control and Prevention and New York City health commissioner. The actual rate will probably be below 1 per cent, Mr Frieden told Bloomberg in an e-mail.

An editorial published in The New England Journal Of Medicine (NEJM) by Dr Anthony S. Fauci and Dr H. Clifford Lane, of the National Institute of Allergy and Infectious Diseases, and Dr Robert R. Redfield, director of the Centres for Disease Control and Prevention, arrived at the same conclusion.

"If one assumes that the number of asymptomatic or minimally symptomatic cases is several times as high as the number of reported cases, the case fatality rate may be considerably less than 1 per cent," the doctors wrote.

"This suggests that the overall clinical consequences of Covid-19 may ultimately be more akin to those of a severe seasonal influenza (which has a case fatality rate of approximately 0.1 per cent)… rather than a disease similar to Sars or Mers, which have had case fatality rates of 9 to 10 per cent and 36 per cent, respectively."

Dr Bruce Aylward, who leads the WHO's coronavirus efforts, expects the fatality rate to turn out between 1 and 2 per cent, The New York Times reported.

Early estimates of the coronavirus death rate in China were about 2 per cent. A more updated report in NEJM based on over 1,000 patients across the country found it to be lower, at 1.4 per cent.

"At this point of time, there is nothing to suggest that the virus has changed in its virility," Singapore's Associate Professor Mak said. "But what has happened is that those figures have continued to change as more information becomes available."

In South Korea - the worst-hit country outside of China and where residents are being checked aggressively for the virus - the fatality rate comes in under 1 per cent. More than 6,000 infections have been detected in the country, and at least 40 people have died from it.

Calculations based only on total current cases and deaths are flawed, The New York Times reported Mr Adam Kucharski, a mathematician at the London School of Hygiene and Tropical Medicine, as saying. He described it as a "statistical illusion".

"(Based) on best available data, when we adjust for unreported cases and the various delays involved, we're probably looking at a fatality risk of probably between maybe 0.5 and 2 per cent for people with symptoms," said Mr Kucharski, who studies how diseases spread.

Asymptomatic cases

About 80 per cent of people infected with the coronavirus exhibit only mild symptoms while some experience none at all, the WHO has previously said. If many cases go undetected as a result, the virus is able to stealthily spread across communities while evading the WHO's tally, which experts use for analysis.

"A lot of people are asymptomatic," Professor Rosanna Peeling, director of the International Diagnostics Centre at the London School of Hygiene and Tropical Medicine, told Bloomberg. "We're only seeing the cases that are confirmed and the cases of people presenting to the hospital because they can't breathe."

As some infected individuals also take more time to present symptoms, hospitals around the world may not have been adequately equipped to detect and treat these patients, according to Prof Mak.

Essentially, it is tough to pinpoint the true extent of the coronavirus' lethality until governments get a better grasp of the situation in their countries and share the information transparently.

"We're not too fussed about whether or not (the death rate) changes over time, because we understand that this is in part driven by the statistics that are available," Prof Mak said.

"What's important is to focus on our own local efforts to make sure that we detect as early as possible every case that comes on, and that we are able to treat them."

The epidemic has infected more than 98,000 people worldwide and killed over 3,300 as of Friday afternoon (March 6).