The state's Chief Health Officer has warned West Australians to expect another "significant wave" of COVID-19 infections within the next six weeks.
While it was hard to predict what the next outbreak would look like, Andy Robertson said Western Australia could expect to see daily COVID-19 cases mirror that of previous outbreaks.
"In our previous peaks, we had an initial peak of around 10 [thousand], and then a further peak of around 17 [thousand], so it's probably going to be in that sort of ball park," Dr Robertson told ABC Radio Perth.
"It may look similar to our previous wave. We could get significant increases in the number of cases we're having and, unfortunately, that will flow into the [number] of people in hospital and, potentially, in ICU."
Dr Robertson pointed to the new Omicron variants of BA.4 and BA.5 as being responsible for the projected wave.
"They're not more severe, or they're not particularly more transmissible than BA.2," he said.
"But they seem to be able to evade the protection from either having had a previous infection with BA.2 or having had a vaccine."
The COVID-19 vaccine and natural infection would still provide adequate protection against serious disease, according to Dr Robertson, but he said it would not necessarily prevent the spread of the two new variants, which he said were slowly becoming dominant.
From Monday, West Australians older than 30 years will be eligible to receive their fourth dose of the COVID-19 vaccine, after recommendations from the nation's peak vaccine advisory body, ATAGI.
Dr Robertson said the fourth dose was important to consider, especially if it had been a while between booster shots.
"Given that a number of people who got their booster shots early, back in November and December, the protection from that will have started to wane."
While Dr Robertson said he doubted restrictions such as lockdowns would be reintroduced, he suggested individuals take their own measures to avoid reinfection.
"We will be strongly encouraging people to wear masks."
State to hit third peak this year
Dr Robertson declared Western Australia was past its peak earlier in the year, after 9,754 cases were reported on March 30.
Having passed the peak and the state's low levels of COVID-related hospital admissions and deaths prompted Dr Robertson to recommend the state government to ease restrictions.
The recommendations sparked a change to the definition of a close contact, which altered who needed to isolate.
In his written advice to Premier Mark McGowan, Dr Robertson said the move might lead to a "manageable increase in COVID cases as people are infected in non-household and social settings".
Daily infections steadily fell following the decision and dropped just below 5,000 in mid-April.
At the end of that same month, the state government announced most COVID-19 restrictions would be lifted on April 29.
That included the mask mandate, capacity limits at venues, the G2G pass system and most proof-of-vaccination requirements.
Health Minister Amber-Jade Sanderson said it was "time for us to live with this disease".
"We've shown that we have worked superbly together, as a community, to manage the pandemic, and now it is time for us to start to return to normal," she said.
Western Australia then saw its next wave of daily infections, which peaked on May 19, when WA Health reported 17,105 COVID-19 cases.
Daily numbers have been on a steady decline since then, falling to a low of 3,434 new cases at the end of June.
