The changes mean people in WA will be required to get tested and isolate if they re-develop symptoms 28 days after recovering from the virus.

The threshold had previously been set at 12 weeks.

West Australians can also now be classified as close contacts of a case after four weeks rather than 12. They are prevented from visiting high-risk settings including hospitals and must return a daily negative rapid antigen test result.

The ACT on Monday also adopted the latest advice from the Australian Health Protection Principal Committee regarding the risk of reinfection.

The committee on Friday issued a statement warning the BA.4 and BA.5 Omicron variants were able to evade immunity and reinfections could occur only less than a month after a previous infection.

WA Chief Health Officer Andy Robertson said the highly infectious variants represented over half of the state's new cases.

"(They) are making up an increasing percentage of our cases, rising to more than 60 per cent of cases in the last week," he said in a statement.

"This means that people who have had COVID-19 should again get tested and isolate if they have symptoms more than 28 days after recovering."

West Australians who test positive are required to isolate for at least seven days.

WA Health reported 4882 new cases and two deaths on Monday. There are 282 people in hospital, up from 226 a week earlier, including nine in intensive care.

Dr Robertson encouraged West Australians aged 30 and over to get their fourth vaccine dose, which Premier Mark McGowan has confirmed will not be made mandatory.

Australian Associated Press