Death rates from COVID-19 varies from 0.0016 to 7.8 per cent depending on people's age group, according to a new study which has made the first comprehensive estimate of the proportion of those with COVID-19 in China who required hospitalisation, and the fraction who died.
The study, published in the journal The Lancet Infectious Diseases, noted that earlier estimates of overall deaths from COVID-19 were estimated to be 0.2 to 1.6 per cent, and for the oldest age group, over-80s, this was thought to be between 8 and 36 per cent.
However, it said, these past estimates had not adjusted for the fact that only people with more severe symptoms are likely to be tested in most countries, or people in quarantine following repatriation to other parts of the world.
The researchers, including those from Imperial College London in the UK, said these numbers do not reflect the true number of cases across populations.
They said, until now, studies have also not estimated the proportion of infections that will require hospitalisation.
According to the current study, which assessed more than 70,000 cases in mainland China, the overall death rate from COVID-19, including those from unconfirmed cases, could be at 0.66 per cent, with the deaths only from confirmed cases at 1.38 per cent.
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However as the pandemic unfolds, outcomes may improve, making it important to revise estimates in the current study, they said.
"This study provides critical estimates on the proportion of people requiring hospitalisation which, when applied to the UK population, enabled us to get a handle on how many people might need to access NHS services," said Neil Ferguson, study co-author from Imperial College London.
The researchers said the death rates from COVID-19 vary substantially with age, ranging from 0.0016 per cent in 0 to 9-year-olds to 7.8 per cent for people aged 80 and above.
They added that 11.8 per cent of people in their 60s, 16.6 per cent of those in their 70s, and 18.4 per cent in their 80s and above may develop symptoms severe enough for hospitalisation.
These rates compare with 0.04 per cent among 10 to 19-year-olds, and one per cent of those in their 20s, the study noted, adding that 3.4 per cent of people aged 30 to 39 may also need hospitalisation.
The rates, according to the research, nearly doubled from 4.3 per cent in 40-49-year-olds to 8.2 per cent in 50-59-year olds.
Based on their analysis, the scientists believe the death rate due to novel coronavirus infection is slightly lower than earlier estimates made for the virus.
However, they said the value is much higher than for previous pandemics such as 2009 pandemic influenza H1N1, which was estimated to be fatal in around 0.02 per cent of the cases.
The scientists warned that as much as 50 to 80 per cent of the global population could be infected with COVID-19, with the number of people needing hospitalisation likely to overwhelm even the most advanced healthcare systems worldwide.
But they said these numbers may change with likely improvement in outcome, making it important to revise the estimates.
"Our estimates can be applied to any country to inform decisions around the best containment policies for COVID-19," said Azra Ghani from Imperial College London.
"There might be outlying cases that get a lot of media attention, but our analysis very clearly shows that at aged 50 and over, hospitalisation is much more likely than in those under 50, and a greater proportion of cases are likely to be fatal," Ghani added.
In the study, the scientists assumed that people of all ages are equally likely to become infected.
They found the greatest number of cases requiring hospitalisation were among people in their 50s, and once they adjusted for the fact that many milder cases go undiagnosed, the hospitalisation rate was estimated at 8.2 per cent.
This number, the study noted, compares to an estimated 18.4 per cent in the most at risk group -- the over 80s.
According to the researchers, 154 out of 743 people in their 40s had severe symptoms, whereas 133 out of 263 people in their 70s had such symptoms.
They said hospitalisation rates were 4.3 per cent for 40 to 49-year-olds compared with 16.6 per cent for 70 to 79-year-olds, and 11.8 per cent for those in their 60s.
This rate was lower for younger age groups with 3.4 per cent of people in their 30s likely to be hospitalised, whereas for people in their 20s the number could be one per cent, the researchers added.
There was only one severe case out of 50 for those aged 10 to 19 and their hospitalisation rate, the scientists said, is 0.04 per cent.
None of the cases analysed in the under-10s were severe, they added.
On average, the researchers said, the time between the first recorded symptoms and death from COVID-19 could be 17.8 days.
Recovering from the disease and getting discharged from hospitals takes an average of 22.6 days, the study reported, adding that without intervention, the number of people needing treatment is likely to overwhelm even the most advanced healthcare systems worldwide.