Coronavirus Australia: The 10 days it takes to know if social-distancing works

Aussies are being hit with new virus restrictions daily. But there is a significant lag time between putting the measures in place and knowing if they work.

Benedict Brook

@BenedictBrook

4 min read

April 3, 2020 - 12:20AM

There is a critical time period of 10 days that shows whether or not our efforts to tackle coronavirus are working.

It is the lag time between new measures being put in place by the government, such as quarantining overseas arrivals, and any impact on the number of new infections.

It’s the difference between a continued steep growth in numbers and a successful flattening of the curve.

And with a new analysis that has mapped the gradual lockdown measures the federal and state governments have put in place, it’s now possible to see how effective those measures have been.

But experts have warned the use of strict measures to bring down numbers is like a “two-person dinghy trying to steer an oil tanker”.

The early indications are that Australia is having some success in “flattening the curve”.

But if local transmission increases, which is likely, it may only be a brief downward turn.

There are now 5107 confirmed cases of coronavirus in Australia with 2298 of those in New South Wales. That state recorded 116 new cases yesterday, a sharp decrease from the more than 200 recorded on Sunday.

Today Prime Minister Scott Morrison said the slowing rate of growth in COVID-19 cases to daily single-digit percentage rises was “welcome”.

Recently returned Australians are being locked in hotels for 14 days. Picture: John Grainger

THE 10-DAY LAG

Australian National University infectious diseases expert Professor Peter Collignon said he was optimistic about the trend but was waiting to see if the curve continued in the right direction.

“If what you had was uncontrolled spread, then those numbers would be going up and up,” he told The Guardian.

He said it generally took five to 10 days to gauge whether any individual government measures has succeeded in suppressing the spread of COVID-19.

That’s reflected in a new paper from Melbourne University, which states it can take anywhere from seven to 10 days.

It could then be another week or so before those severely ill people with COVID-19 require hospitalisation.

“We’re looking at around 10 days from bringing in stricter social distancing measures until we see a change in reported case numbers, and another 11 days, call it three weeks in total after social distancing changes, until we see a change in intensive care unit admission rates,” epidemiologist Professor Tony Blakely said.

That means everyone has to take a breath when assessing the effectiveness of new restrictions. Closing pubs on a Sunday isn’t going to lead to a drop-off in infection rates the next day, or even that week.

“Think of our current measures against COVID-19 like being at the back of an oil tanker and steering it with the rudder of your two-person dinghy,” Prof Blakely said.

“It takes patience for the bow of the oil tanker, in our case, the daily numbers of COVID-19 infections, to slowly turn.”

No laughing matter. NSW Police officers ask a man move on while on patrol at Rushcutters Bay Park in Sydney. Picture: AAP Image/Joel Carrett.

STILL DON’T KNOW IF ALL MEASURES HAVE WORKED

An analysis of the various measures Australia has put in place against COVID-19 infections appears to show some success. Based on a chart by software engineer Ian Warrington, there does appear to be a fall in new cases 10 days or so after some new measures.

Right now, that means we could be seeing some benefit from the borders being closed, which occurred a fortnight ago, but yet to see much effect on mandatory isolation for returning Australians or stricter social-distancing rules that occurred within the past week.

If we go back to early February when non-Australian or permanent-resident arrivals from China were barred entry, we can see very few cases occurred in the weeks after.

However, from early March, infections in Australia began to pick up which is most likely to have occurred because arrivals from other countries – such as Italy, Iran and possibly the US – were importing it.

Initially cases grew relatively rapidly in Australia. But after the ban on arrivals from Italy the rate of growth of new cases appeared to slow.

From mid-March restrictions within Australia began to be imposed including social distancing and the encouragement to work from home.

Then in the past two weeks we’ve seen the closure of pubs and restaurants, reduced gathering sizes and the ban on all non-citizens or residents from entering the country.

By the measure of fewer cases, these restrictions may have worked. Since then, the number of new cases has fallen back from a nationwide peak of 424 new cases on March 24.

Prof Blakely said increasing, or reducing, restrictions was an inexact science.

“Until we have a bit of experience, we don’t really know how much the oil tanker will turn (with a lag) as a result of a nudge versus a panicked throwing of the rudder.

“This is the extraordinarily challenging task of our politicians, chief medical officers and scientists.”

So-called stage three restrictions, which have seen people removed from parks simply for sitting down and people told to leave the home only for essentials, came into force just this week. It might take until Easter to see if they had worked.

LONG HAUL

The big worry now is community transmission. Banning non-citizens from Australia and quarantining arrivals might be successful at eventually halting that pathway for the virus. But if people ignore social distancing rules, it could instead spread very fast locally.

Indeed, of Victoria’s 68 new cases in the last 24 hours, 57 are thought to be within the community.

"(Flattening the curve) will depend on our physical distancing and how well we comply with directions," Victorian chief health officer Dr Brett Sutton said.

He anticipated the virus would not peak in the state until May or June.

The Melbourne University researchers said the numbers were good news but we were still in this for the “long haul”.

Even with successful social distancing measures, and even if they are tightened sometime this month, cases would still rise.

The aim was to ensure admissions to intensive care units (ICUs) were steady over a longer period rather than spike over a shorter timescale.

That model could see the most ICU cases in late May.

“We are some weeks away from peak ICU demand, and crucially that means we have some time left to prepare and work out how to use our dinghy rudder on this COVID-oil tanker epidemic,” Prof Blakely said.

“Not much time, but some time.”