As events are cancelled and the tally of COVID-19 infections continues to rise, many people are asking: "How long is this thing going to last?"

No-one truly knows the answer to that question, but past epidemics and disease forecasting can give us some clues as to what we're in for.

When SARS-CoV-2 was first identified as a mystery virus causing pneumonia in people connected to a market in Wuhan, China, in December last year, experts hoped it would be quickly contained and peter out.

The outbreak of this new virus' closest relative, SARS, in 2002 did cause thousands of infections and hundreds of deaths, but containment efforts, combined with different characteristics of the virus, meant SARS became effectively extinct by 2004.

This new coronavirus is a different story. Experts say it's now looking inevitable that this is a virus that's going to stick around.

And because it's new and no-one's immune to it yet, authorities are working hard to slow its spread to ease the burden on the healthcare system.

That's why countries around the world, including Australia, are bringing in strong social distancing measures. But again: how long for?

We could be looking at up to 12-18 months of this

Countries might be enacting some degree of control measures right through until a vaccine comes along, according to a new modelling study from Imperial College London.

Realistically, that could be 12 to 18 months away.

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In the meantime, the modelling shows that to slow the spread and save lives, multiple measures are necessary, said ABC health broadcaster Norman Swan on Coronacast.

"What they showed was ... if you want to suppress the virus to very low levels, you've got to do a lot," Dr Swan said.

"You've got to do quarantine, you've got to do social distancing and indeed, they say, you've got to shut schools and universities.

"The problem is, once you put your foot on the brake you have no idea when you can take it off, and it might be as long as 18 months."

The modelling is based on numbers for the UK and the US, and while the figures are different to those in Australia, the time frame for a vaccine remains the same.

What goes in to making a vaccine?

Multiple research groups around the world are working on developing a vaccine for COVID-19 using different techniques.

"There are now 15 potential vaccine candidates in the pipeline globally using a wide range of technolog[ies]: mRNA, DNA, nanoparticle, synthetic and modified virus-like particles," said microbiologist Ian Henderson of the University of Queensland.

The US National Institutes of Health have announced that they are funding phase 1 clinical trials of a potential COVID-19 vaccine, called mRNA-1273, which began this week.

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If this seems fast, it's because researchers had already been working on a vaccine to protect against a related coronavirus, which causes Middle East respiratory syndrome (MERS).

Results from this first trial may be available within three months.

But it would still take at least a year for a resulting vaccine to be widely available to the public.

Can't we just shut everything down for a few weeks?

What if we just shut everything down for a few weeks? ( ABC News: Zalika Rizmal )

There have been some suggestions that a complete shutdown for two to four weeks would knock this on the head — short-term pain for long-term gain.

It's a tempting concept, but it doesn't quite stack up, for a couple of reasons.

Firstly, we know the time between when someone gets infected with the new coronavirus to when they start showing symptoms is about five days, on average. Most people who are infected have symptoms within 12 days. But one in 1,000 won't show symptoms until after 14 days.

Then, from a day or two before you start showing symptoms, you're shedding the virus — that is, you're able to infect others. And it looks like the length of time people shed for is about three weeks, but it's been measured at up to 37 days.

So even if we were able to stop transmission entirely on Friday, for four weeks — if every person in every country in the world simultaneously isolated themselves for four whole weeks — it still wouldn't be enough to stop the virus in its tracks.

People who caught the virus yesterday would still be infectious by the time the shutdown lifted.

And of course, a global shutdown is unrealistic. Essential services still need to run, people still need medical treatment, and so on.

That's why health experts warn that even if we brought in an extreme shut-down, the virus would still come back.

"There are very few infections in the world which have disappeared completely," Dr Swan said.

"We are in it for the long haul. This is a major change to the way we live for a long period of time."

