Analysis by the ABC showed about 5.5 million tests are due to expire in the next three months in Queensland and Western Australia alone.
Between one third and two thirds of tests bought by state and territory governments have not been distributed, although figures are unknown in NSW and South Australia as they did not participate in the analysis.
Professor Nancy Baxter, Head of the Melbourne School of Population and Global Health, said it's unreasonable to expect every test purchased would be used however there did not have to be so many left over.
"The approach to providing accessibility to RATs was just overly protective of the resource," Professor Baxter told AAP.
She understood why authorities restricted tests to vulnerable groups in early 2022 when they were hard to find, but believes Australia could have later provided them at shops, pharmacies and other places for free.
Authorities are exploring what to do with excess tests and there are calls to give them away to other countries, but it's unclear how that would work.
"If RATs are near their expiration date you have to make sure that the other countries can actually use them because otherwise they're just going to expire there," Professor Baxter added.
She said RATs remained essential as Australians need them to secure antivirals and were still useful to control the spread of the virus.
Many jurisdictions distribute tests for free in heath care settings and certain public spaces, however they are also widely available to purchase privately in pharmacies and retail stores.
There were 366 COVID-related deaths reported in Australia last week and diagnosed cases have dropped to about 3,100 per day.
Professor Adrian Esterman, Chair of Biostatistics and Epidemiology at the University of South Australia, believes actual cases could be much higher than official figures.
"We've got fewer and fewer people testing themselves, partly because they're not motivated anymore but partly because they can't afford to spend $7-8 a pop on rapid antigen tests," Professor Esterman said.
"We really badly need more testing in Australia... I'd be giving (excess tests) away to Australians."
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