South Australia was one of six Australian jurisdictions which was COVID-19 free during Clive Palmer’s High Court challenge against WA’s ‘all-or-nothing’ approach to its border closure last week.

Since the four-day hearing — where Mr Palmer’s lawyer and the Commonwealth supported the opening of WA’s borders to other states with little to no coronavirus — seeding events have occurred in South Australia and Queensland.

Premier Mark McGowan has previously said he doesn’t trust the border restrictions in place in other COVID-19 eliminated states and wants to keep WA's border closed until community transmission is under control nationally.

Constitutional law expert Anne Twomey said the “moving feast” of changing circumstances in each state meant there had “never been a case like this” in the High Court.

“What’s reasonable and necessary [to protect WA against coronavirus] last week might be different to what is reasonable next week and different again to three week’s time,” she said.

If Mr Palmer is successful in his legal challenge, Ms Twomey said WA would likely have a number of revised border closure directions ready to be immediately implemented.

“If [the state government] did that, it could for example use the Northern Territory and Queensland approach of only excluding people within the last 14 days if they’ve been in a COVID hotspot,” she said.

“Or it could say if you’ve been in a COVID hotspot then you must quarantine for 14 days but we’ll let you in.”

Below is a look at how Melbourne’s second wave has infiltrated states that were considered COVID-19 free during the Clive Palmer High Court challenge:

South Australia

Prior to Tuesday’s potential unknown community transmission case, which remains under investigation, the state hadn't had a mystery case of the virus since April 16, and was in similar standing with Western Australia.

Through the strengthening of its border closures on July 9, Victorians were banned from entering the state unless they were a returning resident. The border then closed to residents on July 28 meaning only essential workers could enter.

The announcement of the border clampdown led to an influx of people trying to cross the Victorian - South Australian border to escape an imminent Melbourne lockdown.

In the past two weeks, 10 positive cases have been detected in the community that are linked to Victoria. Most were self-isolating at home for 14 days when the virus was detected, however at least one case has leaked into the community through close contacts and created a cluster.

The state has moved to cap home gatherings to 50 people and weddings to 100 people, in light of the recent spike in cases.

SA Chief Health Officer Nicola Spurrier described the surge as “very concerning”.

“The thing is with this disease you only get one chance and we need to do everything possible to reduce that community transmission before it gets away from us, and before we can contain it,” she said.

“We’re starting to see the cases mount up now in South Australia. It’s not surprising because we are adjacent to Victoria."

Queensland

Queensland has not recorded a case of unknown community transmission since May 2, however in late-July, two young women allegedly breached quarantine rules by re-entering the state from Melbourne without completing 14 days hotel quarantine.

The women were active in the community for eight days before their infections were detected and have so far passed the virus onto three other people.

No cases of unknown community transmission have been detected, and testing numbers at COVID clinics have surged in recent days in response to attempts to contain the spread.

The breach revealed weaknesses in the Queensland’s border controls with New South Wales, which largely rely on returned residents filling out their border declaration passes honestly.

Queensland’s border has been closed for much of the pandemic. It reopened on July 10 to all except those in COVID-19 hotspots. Residents wanting to return home from high-risk areas must hotel quarantine for 14 days at their own expense on arrival.

As of Tuesday, it had maintained its elimination status, which by definition means 28 days without a case of unknown community spread.

Tasmania

Tasmania has had its border closed for much of the pandemic. It is allowing residents to return home, however they must complete 14 days hotel quarantine upon arrival at their own expense.

Through this process, two cases have been detected in women returning from Victoria since the state’s second wave struck.

To Tuesday, it had maintained its elimination status.

Northern Territory

The Northern Territory has never recorded a case of unknown community transmission. Its borders were shut for much of the pandemic, but were lifted on July 17. Those entering from COVID-19 hotspots must complete 14 days hotel quarantine upon arrival at their own expense.

Through this process, three cases have been detected since Victoria’s second wave.

To Tuesday, it had maintained its elimination status.

The ACT

Prior to a recent cluster of cases, the ACT had not had a community case of coronavirus since
May. It closed its border to Victoria on July 3.

As of Tuesday, it had retained its elimination status.

Western Australia

Western Australia has had its border closed since April 5, however, through exemptions, it was allowing on average nearly 3300 interstate travellers into the state each week.

On July 9, the border with Victoria was tightened to only allow essential workers. Tighter restrictions for New South Wales followed shortly after.

To Tuesday, it had maintained its elimination status.

Victoria and New South Wales have uncontrolled community transmission, with all states closed to Victoria and most also closed to New South Wales COVID-19 hotspots.