Western Australia has recorded four new cases of coronavirus, with three of them linked to the Artania cruise ship, as the State Government pinpointed the start of May as the earliest point restrictions may be eased.

Key points: Just one more West Australian has tested positive for COVID-19

Just one more West Australian has tested positive for COVID-19 Three more cases from the Artania take the state's total to 527

Three more cases from the Artania take the state's total to 527 The WA Premier says restrictions will be reviewed in a few weeks

Health Minister Roger Cook said the four additional cases, all recorded in Perth and aged between 31 and 58, took the state's total number of positive tests to 527.

He said in addition to the three latest Artania cases, the fourth was a close contact of an existing case.

WA COVID-19 snapshot Confirmed cases so far: 661

Confirmed cases so far: 661 Recovered: 648

Recovered: 648 Deaths: 9

Deaths: 9 Total tests: 392,908 Latest information from the WA Health Department





There are 32 people infected with COVID-19 in Perth hospitals, with 12 of those in intensive care.

A total of 296 people have now recovered after testing positive to the virus.

"This is more than half of our confirmed cases, so that's extremely pleasing," Mr Cook said.

He said the total number of WA cases linked to cruise ships stood at 209, including 53 from the Ruby Princess and 75 from the Artania.

Mr Cook said the State Government was confident the Artania would be able to leave Fremantle Port by the end of this week.

"Everyone has now been isolated in their own cabins. We're confident that the people who are getting sick are those who were always going to get sick," he said.

"That is, they contracted the disease before the new arrangements went into place."

The coronavirus-infected cruise ship Artania docked in Fremantle more than two weeks ago. ( AAP: Richard Wainwright )

The Minister said the Australian Border Force had ordered the ship to leave Australian waters by this Saturday, April 18.

Around 400 crew members remain on board the ship after it docked in Fremantle following an outbreak of the virus last month.

Premier Mark McGowan said all bar one of the seven cruise ships the Government was keeping an eye on as they travelled through WA waters had now passed Geraldton.

"That one ship we expect will go past Fremantle and keep on going, so that resolves that, we hope," Mr McGowan said.

First review of restrictions in May

Mr McGowan has flagged May 1 as the earliest date the State Government would consider relaxing any coronavirus-related restrictions.

WA Premier Mark McGowan says his Government will review the restrictions monthly. ( ABC News: Hugh Sando )

He told 6PR radio Western Australia's diagnosed case numbers remained low, but the easing of any measures currently in place would be considered over a "long period of time".

"We're doing pretty well but you don't want to take the foot off the pedal before such time as you know you can," he said.

"We'll review it monthly. The first major review will be coming up in a couple of weeks."

Mr McGowan said that would be the opportunity to consider the long-term case results and whether any restrictions could be eased.

"I would have thought around the 1st of May, if we were to do anything, would be the time," he said.

Later in the day, Mr McGowan said any "tweaks" would be made in a methodical and measured way based on health advice.

"The restriction I am not going to let up on, certainly in the near-to-medium term, is the interstate border," Mr McGowan said.

"Because I think the interstate border gives us the capacity to drive down the spread of the illness in Western Australia."

The Premier praised the behaviour of West Australians over the Easter break but urged people to continue to follow the rules.

"If we get health advice that we can lift any of the restrictions, well then that's the time to do that. But up until then, [people should] do the right thing," he said.

Mr McGowan said 36,896 people were stopped at regional border check points over the long weekend.

Only 876 people were denied entry into another region and turned around.

"And just three on-the-spot fines were handed out for breaching COVID-19 related directions over the weekend," Mr McGowan said.

Mr Cook said there was no deadline on decision-making around whether restrictions could be eased.

"This isn't a hard science. In some respects this is an art, the art of public health," he said.

"If we see the situation of sustained low numbers over a period of time, well then we'll need to look at what restrictions we can ease."

"The storm still sits off our shores while we don't have a vaccine."

School decision due this week

A decision on what Term 2 will look like for schools across the state will be decided later this week.

The State Government was optimistic on Tuesday that there was a good case for schools to go back – in some form.

"How we do it and what we do, it'll be safe. But it'll have a strong focus on making sure we provide education for our young people," Mr McGowan said.

WA joins tuberculosis vaccine trial

Meanwhile, thousands of WA healthcare workers will participate in a nationwide trial to test whether an existing vaccine normally used to combat tuberculosis could be used to boost immunity against COVID-19.

The BCG vaccine is already known to boost immunity against a range of infections. ( ABC News )

"At least 2,000 WA healthcare workers will help test whether an existing tuberculosis vaccine can reduce their chance of COVID-19 infection, lessen the severity of symptoms and boost immunity," Mr Cook said.

"When they receive their standard influenza vaccine half the participants will also receive a BCG tuberculosis vaccine.

"It seeks to establish whether BCG vaccine, which is known to boost immunity against a range of infections, has a similar effect on COVID-19."

The trial will feature 750 frontline staff from Fiona Stanley Hospital, 750 from Sir Charles Gairdner and 500 from Perth Children's Hospital.

The trial will involve 750 workers from Fiona Stanley Hospital and staff from two other Perth hospitals. ( ABC News )

Mr Cook said mining billionaire Andrew Forrest's Minderoo Foundation had committed $1.5 million to help the Telethon Kids Institute roll out the project in WA.

Institute director Jonathan Carapetis said the vaccine had been around for the best part of a century.

"About 20 years ago we discovered something else about the BCG vaccine which is that it appears to offer broader effects beyond just preventing tuberculosis," Professor Carapetis said.

"It appears to also prevent the incidence of other infections, particularly respiratory infections.

"That … got us to think around what sort of non-specific effects in boosting the immune system might we be able to take advantage of with this vaccine, to prevent the most vulnerable in our community getting coronavirus or getting it severely."

People without any symptoms may be tested

Mr Cook also told 6PR the state was considering a more "aggressive" testing regime to include even people who were not showing symptoms.

The Minister said it was the result of increased testing resources and the capability of the state's private pathology clinics.

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"We really have a … unique opportunity to now start looking everywhere for the virus," he said.

"So rather than trying to fend it off when people present to us with symptoms, where do we now actually go and seek it out to really get on the front foot and be really aggressive?"

Mr Cook said expanded testing would help to develop the state's evidence base.

"No one will thank the Government for releasing the current restrictions if we then see another outbreak of the disease. So we have to take these measures very carefully and very slowly," he said.

"The best way we can do that is to follow the best medical advice, and the best medical advice is based upon the best evidence.

"So we are really going to build the evidence base up so that as a community, we are in an even stronger position."