Premier Mark McGowan has doubled down on his hardline COVID-19 rules which have frustrated West Australian business leaders and led to one case closing an entire Perth primary school.
Dozens of teachers, students and parents face 14 days in quarantine after a teacher tested positive at Winterfold Primary School in Perth's southern suburbs.
The school kept its doors closed on Wednesday to allow for deep cleaning.
It will reopen on Thursday but with replacement teachers after isolation rules wiped out virtually all of the facility's staff.
Education Minister Sue Ellery said the infected teacher had attended a professional development day on Friday with 55 other staff.
They will all be required to quarantine for 14 days, along with 27 children who shared a classroom with the teacher on Monday.
The children's parents, and in some cases other household family members, will also have to isolate.
Ms Ellery had last week declared schools would be the "last to close" during WA's Omicron outbreak, which grew by a further 17 local cases on Wednesday.
She defended the government's policy settings, insisting there was a pool of about 4000 relief teachers ready to step in during future outbreaks.
"The particular circumstances here are that the whole of the teaching staff attended the professional development day on Friday. That doesn't happen every day," she told reporters.
But WA Principals Federation president Bevan Ripp told ABC radio the pool of relief teachers had already been "absolutely decimated".
The McGowan government's refusal to say when the borders will reopen or when close contact definitions will change has frustrated the business community as Omicron continues to spread.
Qantas chair Richard Goyder and Wesfarmers chief executive Rob Scott are among the local heavyweights who have publicly criticised the premier, saying they will relocate to the eastern states to escape his policy settings.
International students have been left in limbo after being given just days to arrive back into Australia to be deemed eligible for entry to WA.
Mr McGowan has also faced blowback from the powerful resources sector after the virus spread to mine sites operated by BHP and 29Metals this week.
The premier has promised isolation periods will be halved for COVID-infected people and their close contacts but only when the state reaches a yet-to-be defined higher caseload.
"It won't be far away," he said on Wednesday.
"But just so you understand, the 14 days is safer. It ensures we have less spread of the virus in Western Australia, it allows us to get our third dose vaccination rate up without greater community spread of the virus.
"What we've done has saved thousands of lives and many thousands of jobs, and that's the approach we will continue to adopt."
The premier said WA's policy settings had made the resources sector the "most successful in the world" during the pandemic.
"At the moment, there's been really no disruption to that industry," he said.
The government will make additional vaccination bookings available this month in a bid to improve WA's third dose rate, currently at 37.6 per cent.
