Coronavirus isn't the first pandemic to sweep the globe in recent years. Epidemics like bird flu, Ebola, SARS and swine flu are still fresh in our memories.
So how does COVID-19, the disease caused by coronavirus, compare? And what sets it apart from the flu seasons we face each winter?
Here's how Dr Norman Swan, host of the ABC's Coronacast, explains it:
"COVID-19 has two or three times the transmission rate [compared with the flu] … and the case fatality rate for COVID-19 is around 30 times higher than the flu."
How contagious is coronavirus?
Diseases further to the right in this chart have a higher reproduction rate, which is the average number of people an infected person will spread the illness to.
As we can see in the chart, coronavirus spreads more easily than seasonal flu. The reproduction rate (also called "R0" or "R naught") is somewhere between 2 and 2.6. It's shown as a range because it varies between places and is influenced by the measures taken to slow transmission.
By contrast, each person who gets seasonal flu will pass it on to just over one other person on average, meaning it spreads much more slowly across the population and ultimately infects far fewer people.
The goal with a pandemic is to get the reproduction rate to less than one, at which point the virus runs its course in the population.
We can see that SARS is more contagious and significantly more deadly than COVID-19.
However, SARS is easier to control because infected people aren't at their most contagious until the second week of their illness. Since they start showing symptoms before then, they can be quarantined before they're most risky.
With COVD-19, you can be contagious even before you show symptoms (up to 24-48 hours before, according to the World Health Organisation), although most transmission happens after symptoms appear. If there is a lag between symptoms appearing and getting a diagnosis, you could be infecting others during that time.
The virus can also be transmitted via contaminated surfaces, but this isn't the main way it spreads.
We don't yet know whether it's possible to catch coronavirus multiple times.
How deadly is COVID-19?
The higher a disease is in the chart above, the more deadly it is.
This coronavirus is a new virus so we can only estimate the fatality rate of COVID-19 in these early stages.
Based on what we can see so far, COVID-19 is far less deadly to infected patients than Ebola or MERS (Middle East respiratory syndrome, another novel coronavirus). However, the fact that this coronavirus is so contagious and has crossed borders means significantly more people are expected to die.
For example, Ebola has killed about 11,300 people since its outbreak, a figure that COVID-19 has already surpassed. By contrast, NSW is preparing for 8,000 to 12,000 COVID-19 deaths this winter alone, using fairly conservative estimates from NSW Health for how many people it will reach (20 per cent of the state).
Deputy chief medical officer Paul Kelly told reporters he anticipates a 1 per cent death rate for Australiaand Chief Medical Officer Brendan Murphy has previously said it "could be lower".
With a 1 per cent fatality rate, if the virus were to reach any more than 40 per cent of the population, it could see more Australian lives lost than in both world wars combined.
If the death rate were to climb to 1.75 per cent, we'd see this outcome even if the virus infected 20 per cent of Australians.
There is no guarantee though that the virus will reach this many Australians.
The fatality rate is not fixed
The fatality rate for COVID-19 varies depending on how old the patient is, their general health and whether they can receive intensive care.
When there aren't enough hospital beds, staff, or equipment like ventilators, more people die. This is what's playing out in Italy right now, where the fatality rate is at least five times higher than in Singapore.
We don't yet know what Australia's fatality rate will be, but it will be partly determined by the infection rate across the population.
While health departments are purchasing more ventilators and converting more hospital beds to intensive care beds, there is a risk that we won't be able to scale up enough to meet demand. The faster and higher the infection rate, the more likely it becomes that hospitals get overwhelmed.
Australia has just over 2,200 ICU beds nationally with almost 900 in NSW, which NSW Health plans to double. With a 20 per cent infection rate, about 254,000 Australians would require intensive care this winter.
The "overwhelm" factor means fatality rates will likely vary from state to state and week to week in Australia. For example, the fatality rate in Wuhan in February was 5.8 per cent compared with 0.7 per cent in other areas of China.
In the early stages of the outbreak in China, the fatality rate hit 17.3 per cent but has reduced over time to 0.7 per cent.
The fatality rate for COVID-19 is also influenced by your age, rising to 21.9 per cent for people over 80.
It is also higher for people with underlying health conditions and respiratory issues.
What this chart doesn't show
Deadliness isn't the only measure that matters. It's also worth considering long-term health implications.
We don't yet know whether COVID-19 does lasting damage to the body for the approximately 98 per cent who recover.
Doctors from the Hong Kong Hospital Authority say they've observed reduced lung capacity in some recovered patients but their sample group was too small to draw wider conclusions.
With knowledge of the disease's impacts still evolving, it is critical to slow the infection rate to avoid an exponential increase in cases and deaths in Australia.
About the data:
Estimated range for the coronavirus basic reproduction rate (R0) is taken from research by the COVID-19 Response Team at Imperial College, London. The coronavirus crude fatality ratio (CFR) is taken from estimates by the World Health Organisation's Joint China Mission report. Please note the limitations of estimating fatality rates while an epidemic is still unfolding.
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