The death rate for people infected with coronavirus is “significantly ramped up” among people over the age of 80, officials said.
England’s chief medical officer Professor Chris Whitty said that overall around 1% of people who become infected “might end up dying”.
The government’s new battle plan for tackling the virus states that the elderly and people with pre-existing illnesses would be at highest risk.
Worst-case scenario planning has estimated that up to 80% of the population could become infected.
But Prof Whitty said the figure was likely to be much lower.
The Covid-19 action plan states that among those who become infected, some will exhibit no symptoms and other will have a “mild-to-moderate self-limiting illness”.
But a minority of people could develop complications – such as pneumonia – severe enough to require hospital care.
“In a small proportion of these, the illness may be severe enough to lead to death,” it states.
The document adds that “the risk of severe disease and death increases among elderly people and in people with underlying health risk conditions”.
Following the launch of the action plan, Prof Whitty said: “Overall, probably around 1% of people who get this virus might end up dying based on the Chinese experience.
“To be clear that therefore means 99% of people will not.
“If a higher proportion than we are currently aware of, get the infection without any symptoms that mortality rate will go down.
“But let’s take 1% overall as the current reasonable figure. It goes up a bit in people who are older and more vulnerable. It will be much lower than that in younger people who have no other health problems.
“The bit of information we don’t know – the proportion of people who have no symptoms at all. And the second thing we cannot be sure of is what proportion of the population can get infected.
“It will not go above 80% – for planning purposes of course we go up to the highest rate that it reasonably could – but in my view the proportion of the population that get infected is likely to be lower than that and probably a lot lower.”
He added: “There is a significant ramp up in the risk of people dying with this infection once they get over 80. It begins to take off a bit earlier than that.”
But Professor Whitty stressed that the “great majority” survive coronavirus, even among the elderly.
“Even for the highest risk group, the great majority of people will survive this.
“If you look at the Chinese data, if you take the very oldest people, the great majority survive.”
He added: “If you’re talking about the low-risk groups, the rate of mortality is well below 1%.”
Prof Whitty added that evidence suggests that the illness is mild among children.
Dr Tedros Adhanom Ghebreyesus, director-general of the World Health Organisation (WHO), said on Tuesday that globally about 3.4% of reported Covid-19 cases have died.
But experts in the UK said the figure could be an overestimate.
Professor Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh, said: “Calculating the death rate for Covid-19 is not straightforward. We believe that we have a good count of the number of deaths among people infected with the virus. That’s the numerator.
“But we do not believe that we have a good count of the number of infections. That’s the denominator. The WHO is using the official figure for confirmed cases as the denominator, and this gives the estimate of 3.4%. But if a significant number of mild cases have been missed or not reported then this estimate is too high.”
Professor Paul Hunter, professor in medicine at the University of East Anglia, added: “Current quotes are estimates based on currently available data with assumptions or models where we do not have exact data.
“Ultimately 1-2% is an estimate based on a number of assumptions which may or may not be true. But in my view 1-2% is still a reasonable estimate.”