If you're a younger adult who's comforted yourself with the idea that if you were to get COVID-19, it probably wouldn't be too bad, don't be complacent.

Yes, studies continue to show that the older you are, the more likely you are to die from COVID-19 — especially for people with other conditions like diabetes and coronary heart disease.

But health experts are warning that it's not impossible for younger adults to have a severe form of the disease or even die from it, even those who don't have any other obvious risk factors.

Bruce Aylward, who led the World Health Organisation's recent mission to assess the pandemic in China, said his team found there had been many deaths in people without other health conditions, and in people decades younger than the groups deemed most at risk.

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"In some areas there were less than 50, less than 20 per cent who [local healthcare workers] could identify had comorbid conditions," Dr Aylward said.

"Indeed, people who did have comorbid conditions had a much higher ratio of dying from the disease, but in most people there were no other predictors, apart from age, that they could die.

"I would also emphasise that there were a lot of people in their 30s, 40s, 50s, who were dying as well," said Dr Aylward, speaking in a webinar for Australian health protection officers earlier this month.

Even though the proportion of younger people having severe outcomes is small, that can still scale up to a significant number because of the size of the COVID-19 pandemic, said physician and health reporter Norman Swan on the ABC's Coronacast.

He said it was a worrying situation that's played out in China and elsewhere.

"Intensive care units across China and across Italy are full of people who are young. And it's the young who are dying with no obvious risk factors," Dr Swan said.

"When this takes off, it's young people who hit your intensive care units and you're making decisions between a 40 year old and a 60 year old ... terrible ethical conditions.

"And when you look at the 30 and 40 year olds who are dying, they don't have heart disease, they don't have diabetes, they don't have obvious risk factors. So there's a random element here."

Treat numbers with caution, but don't be complacent

Brian Oliver, a respiratory infectious disease expert at University of Technology Sydney, interpreted the numbers with more caution but said we couldn't afford to be complacent, because the risk for vulnerable groups was so high.

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"Only 1 per cent of the people who died were otherwise healthy [in China]," Dr Oliver said.

"But with any infection, it's a bit like a lottery. Because we haven't had these infections before, how our body responds to it is completely unknown.

"There's always going to be people who have no apparent risk factors and do very badly."

Dr Oliver said the proportion of deaths in younger people seemed slightly higher in China than in other countries.

"What happened in China doesn't seem to be playing out in quite the same way elsewhere. In terms of younger people being susceptible, it seemed to be happening a lot more in China but not so much elsewhere and I don't quite understand that," he said.

"It might just be a numbers thing – that the numbers were so much bigger in China and you pick up on some more of these small signals."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 3 minutes 57 seconds 3 m 57 s Dr Norman Swan explains coronavirus terminology

Everyone has a part to play for the greater good

Dr Swan reiterated that the death rate was higher among older people, but said the overall numbers of young people in intensive care or dying had been "a surprise for many people".

He emphasised that the risk is still low to individual Australians, but these cases were a warning that everyone needs to act to help control the epidemic.

Dr Oliver agreed.

"It's a bit like a war situation. Everyone's called to arms for the greater good," he said.

"If you feel like you've got a cold or flu, self-isolate. Call a doctor and get advice before you do anything else. Don't go to work. Don't soldier on."