Chances are if you get sick from the latest coronavirus you'll get a pretty mild illness.
About 80 per cent of people with COVID-19 will have a "mild to moderate illness that lasts about two weeks," said Sanjaya Senanyake, an infectious diseases specialist from the Australian National University.
However, some people will develop more severe disease with COVID-19.
According to the World Health Organisation, 15 per cent of coronavirus cases are severe infections that require oxygen, and 5 per cent are critical infections, requiring ventilation.
"For COVID-19 at the moment, the global case fatality rate is over 3 per cent, although we think it's probably closer to 1 per cent," Dr Senanyake said.
But the true mortality rate will take some time to fully understand, as there are many mild cases likely not yet reported.
How the virus makes people sick
The first thing to know is that viruses work by hijacking the machinery inside your own body's cells to make more copies of themselves.
Infection activates the immune system leading to, among other things, inflammation.
Some people will be symptom-free, others will get a fever, cough and other symptomsas the immune system kicks in to fight the virus.
But things get more serious when people start to experience fatigue and shortness of breath.
Immune system over-reaction
When people get a large dose of the virus this can overwhelm the immune system, which overcompensates with inflammation that spirals out of control.
This results in viral pneumonia, where air sacs (alveoli) in the lungs fill with fluid and it becomes difficult to breathe.
"If you have something like a boil you get a lot of fluid and if that's happening inside your lung ... then that clearly interrupts exchange of oxygen between the atmosphere and your blood," says medical virologist Professor William Rawlinson from the University of New South Wales.
The virus infection also damages the lining of the lung so bacteria can invade more easily.
And as with influenza this can lead to a secondary infectioncalled bacterial pneumonia. While this can be treated with antibiotics this can also contribute to death.
On top of this, falling blood oxygen levels also put pressure on organs like the heart.
And in severe cases, the viral or secondary bacterial infection can go into the bloodstream and shut down other organs in the body, including the kidneys.
Serious infection can also cause a fall in blood pressure that can affect multiple organs.
And in the late stages of infection you can die from cardiac arrest from the virus directly attacking the heart.
On ABC's Coronacast recently, Dr Norman Swan, also pointed to evidence that the coronavirus that caused the 2003 SARS outbreak affected the respiratory centre in the brain which actually drives your breathing.
The people in the community most at risk for COVID-19:
- people who have recently been in a high risk country or region (mainland China, Iran, Italy or Korea),
- people who have been in close contact with someone who has a confirmed case of COVID-19,
- elderly people,
- people with chronic medical conditions,
- people who have compromised immune systems,
- Aboriginal and Torres Strait Islander peoples (as they have higher rates of chronic illness).
Epidemiologist Professor Robert Booy of the National Centre for Immunisation Research and Surveillance (NCIRS) says while most people infected will have a mild illness, the older you are the greater the risk of it killing you.
"The other thing that loads the risk on top of being old is those chronic conditions like diabetes, heart disease, hypertension. If you have [these conditions], and you're elderly, you're in trouble," he says.
But some younger people in their 30s, 40s and 50s are still dying from the virus.
But health experts have warned younger adults shouldn't be complacent about their risk, as it's not impossible for them to have a severe form of the disease or even die from it.
While children are key drivers of influenza transmission in the community, initial data from the COVID-19 pandemic suggests children are far less affected than adults.
Professor Rawlinson says when people get life-threatening infections the aim is to support them intensive care — this involves using a ventilator to help them breathe, and if needs be later a heart-lung machine.
But he says older people — especially those with existing heart and lung disease — are often too frail for such interventions to avoid death.
Even if they are not too frail, older people might miss out on life-saving care if we get to the stage where there are not enough hospital beds to go around.