Chief investigator Calum Semple, professor in child health and outbreak medicine at the University of Liverpool, said coronavirus is an "incredibly dangerous disease".
He said: "Crude hospital case fatality rate is of the same magnitude as Ebola. And people don't get this.
"If you come into hospital with Covid disease and you're sick enough to be admitted, crude case fatality rate is sitting somewhere between 35 and 40 per cent.
"That's the same case crude case fatality rate for someone admitted to hospital with Ebola."
Sixty per cent of those admitted were male, and women were 20 per cent more likely to survive.
The research, which has yet to be peer-reviewed, found that almost half of cases did not have any underlying factor or extra risk such as obesity. But when patients admitted to hospital were obese, their risk of death rose by 37 per cent.
THE UNDERLYING CONDITIONS
Conditions which increase risk to survival for patients hospitalised with Covid-19
Dementia: increases death risk by 39 per cent
Obesity: 37 per cent
Chronic heart disease: 31 per cent
Chronic kidney disease: 25 per cent
Chronic pulmonary disease: 19 per cent
Presence of tumours: 19 per cent
Source: Features of 16,749 hospitalised UK patients with COVID-19 using the ISARIC WHO Clinical Characterisation Protocol, April 2020
Semple said those who were obese with a body mass index (BMI) over 30 "do particularly badly from Covid disease, so they're more likely to go on to the intensive care units and to go on to die".
There were many reasons why obese people may have a "very tough ride" if they catch the virus, he added.
"Nobody who is a big person is just a big person in isolation," he said. "But the disease will cause problems in their lungs, and hearts and kidneys for complex reasons because fat cells secrete chemicals that essentially increase the inflammatory state of the body."
He said it was also striking that the disease affects men much more than women, with the differences rising with age.
Those with dementia had death rates 39 per cent higher than other patients, while heart disease patients faced a 31 per cent increase in risk. Death rates in patients admitted over the age of 80 were 14 times as high as those among the under-50s, and risks for those in their 70s were 10 times higher than for those under 50.
Semple praised the majority of Britons for sticking to the lockdown, but said: "Still we see isolated egregious examples of selfishness, where people think it's okay to meet up in the park and share a four-pack of beer, and I've seen it happen.
"And the attitude particular groups of younger people are taking is: 'All right Jack, this doesn't bother me, why should I be worried.' They just don't understand that they're just as likely to catch it and transmit it, and that will affect the rest of society."
The study tracked 16,749 patients admitted to hospital with Covid-19 in England, Scotland and Wales between February 6 and April 18 this year.
Just 2 per cent of patients were under the age of 18, including 1.1 per cent under the age of 5.
