Face masks will remain mandatory for West Australians despite a new study suggesting most COVID-19 cases are being detected.

The number of active cases has steadily fallen over the past week to 45,766, with around one in five PCR tests still coming back positive.

WA Health reported 7998 new cases on Thursday, while 256 people were in hospital including eight in intensive care.

WA’s PCR positivity rate has been consistently high during the Omicron outbreak, fuelling the belief the virus had spread much further than case numbers indicated.

But a new study by the Telethon Kids Institute suggests otherwise.

Researchers visited 296 Perth households and tested 396 volunteers for the virus, none of whom were positive.

Lead researcher Nick Golding said it likely reflected WA’s very high vaccination rates and test availability.

“This data suggests that around three quarters of all infections are being detected by the health system, which is higher than had been expected,” Professor Golding said.

“It means disease modellers and government can be confident that there is not a huge proportion of undetected COVID-19 lurking in Perth.”

The state government has provided free rapid antigen tests to all households, while long queues at PCR clinics have largely been avoided.

Premier Mark McGowan said he was surprised but heartened by the result.

“We’re the only government in Australia that has given households free RATs across the board and that’s obviously paying dividends,” he told reporters.

About 60 per cent of Thursday’s new cases were confirmed by self-reported positive RATs.

Modelling by the Telethon Kids Institute and Curtin University suggests about one third of West Australians will be infected in coming months.

Scrapping mask-wearing except for in hospitals and aged care homes would lead to about 150 more deaths between Easter and the end of July, the modelling assumes.

Mr McGowan said the government hadn’t decided when mask mandates would be removed, including for children in year three and above.

“We know that masks work, they reduce the spread of the virus, they reduce the pressure on our hospitals,” he said.

Researchers expect the proportion of cases reported in younger people to decrease over time.

“They are the first infected because of their large contact networks, with infections in older populations becoming increasingly common later in the outbreak,” Associate Professor Ewan Cameron said.

– AAP