Aaron Worker has no immune system - and he's terrified of COVID-19

None.

At all.

The young father had a heart transplant almost exactly a year ago.

If he had any sort of functioning immune system to speak of, it would attack his new heart and reject the transplant.

The medication he takes keeps him alive, precisely through keeping his immune system out of action.

But having no immune system means if he catches the coronavirus, it could be deadly: there is nothing in his body to fight it off.

Mr Worker said during this period he was "quite scared to leave the house".

"We try to shop during non-built-up hours normally - like, during the day when there's not many people there," he said. "At the moment, that's not really possible."

'We have plenty of hand sanitiser at the moment, but we will run out. If there are people with like, 20 bottles ... I mean, we're the ones who really need it."

And he said it was "very frustrating" to see people disobeying directions from public health experts to self-isolate as much as possible.

"No one who has had a transplant has contracted [the coronavirus]," he said. "So they don't know how it could potentially affect us.

"That's what we're worried about. With the normal flu, our bodies can't fight it but they can give us stuff to get over it.

"We don't really want to find out [what happens with the coronavirus]."

His request to the community is simple: don't be silly, use common sense, and wash your hands.

For the general population, the risk of dying from coronavirus has been between 1 and 4 per cent, depending on the country and the quality of healthcare in that country.

The risk of dying varies by age. People aged 0 to 40 have an 0.2 per cent chance, whereas people aged over 80 have an almost 15 per cent chance of dying if they become infected.

Having a pre-existing condition raises that possibility further: for heart disease, there is a one in 10 chance of dying if the person contracts the illness.

For people with suppressed immune systems, it is not known exactly what the fatality rate is expected to be but all health experts are in agreement that there is a good chance the coronavirus could be fatal.

This is because at the moment, the human body's natural immune system is the only weapon we have that works against the coronavirus.

It's not just transplant recipients like Mr Worker who have no immune systems. Cancer patients who are going through chemotherapy have severely compromised immune systems, because the treatments limits their bodies' ability to produce white blood cells.

People with an autoimmune disease, such as lupus or fibromyalgia, are at a higher risk from the coronavirus no matter their age. An autoimmune disease is one in which the immune system mistakenly attacks normal parts of the body like cells, tissues and organs, and around five per cent of Australians have one.

It's also a known fact that people without any symptoms can be carriers for the coronavirus. If they are carrying on their lives as normal, they can infect others who are at a higher risk of having severe symptoms or dying.

When researchers tested one entire small town in Italy this month - Vo, with a population of just under 3500 people - they found six "asymptomatic carriers": perfectly healthy-seeming people with no idea they had the virus, who were passing it onto others.

Dan Lowe, chief executive of Eskleigh Support and Disability Care Tasmania, estimates that 80 to 85 per cent of their residential clients have an underlying health condition that makes them a higher risk for severe symptoms or fatality if they were to catch the coronavirus.

They have implemented thorough measures to prevent spread among their clients and staff, but "we can't control how the public are reacting".

"I don't think people are taking it seriously enough," he said.

"It's understandable - I think a large part of people's anxiety is that their way of life has changed so quickly, that their brains haven't caught up.

"But in Tasmania we're very lucky, we're in a unique situation in being able to isolate.

"[Eskleigh] can't control what people are doing, if they're still congregating and not following those social distancing recommendations - we can only keep educating our clients about the risk and make sure our staff are following the right procedures to reduce the spread of Covid-19."

Peter Bourne, who lives in Bridport and has underlying health conditions, said his friends keep showing up to his house as if everything was normal.

"We had one turn up here today and I sprayed his hands," he said.

"It's pointless us taking all the precautions when you have friends turn up who don't. It's scary."

He has heart and lung problems and was going to book in for surgery to get a pacemaker - but "the last place I want to be at the moment is a hospital".

"So I'm happy to wait that out," he said. "We just don't know, and I think that's what's frightening everybody who's health-compromised.

"We've just never experienced this before - things like going to the chemist and them, 'the order's not in'.

"We're only human after all; we are frail beings."

For Mr Worker, he was due to travel to Melbourne this month for his very last scheduled biopsy, marking a year since his transplant - although it's in doubt if he'll go at the scheduled time now.

The biopsy was expected to show that his body has accepted the transplant.

"I haven't had any rejection at all, it's just been perfect," he said.

When the COVID-19 pandemic is over, that's the first thing he'll be celebrating.