Research from the Australian National University estimates 70,000 Australians may have been exposed to COVID-19, around seven times more than the current known number of cases.
A team of researchers led by Associate Professor Ian Cockburn and Professor Elizabeth Gardiner, developed a blood test that screens for antibodies the immune system produces to fight SARS-CoV-2, the virus that causes COVID-19.
The presence of those antibodies in the blood may suggest a previous infection.
Between June 2 and July 17, researchers screened 3000 blood samples from people across Australia who had not been identified as COVID-19 positive before.
It found eight in 3000 healthy people may have been previously infected with COVID-19.
"Our best estimate is that around 0.28 per cent of Australians - one in 350 - had been infected with SARS-CoV-2 by that time," Associate Professor Cockburn said.
"This suggests that instead of 11,000 cases we know about from nasal swab testing, about 70,000 people had been exposed overall."
"Estimating how many people have had SARS-CoV-2 enables us to better understand the spread of the disease and how effective community testing is, and can determine if there is evidence of herd immunity."
While the study is not yet peer reviewed, John Curtin School of Medical Research director Professor Graham Mann is optimistic about the study's findings.
"These highly sensitive ways of detecting antibodies are going to find many uses, especially in surveying for spread in the community, especially among people without symptoms," Professor Mann said.