A new study has found the number of Australian adults infected with COVID-19 at the end of February, was at least twice as high as cases reported to authorities.

At least 17 per cent of adults are estimated to have recently been infected with SARS-CoV-2, the virus that causes COVID-19, with the majority of these infections believed to have occurred during the Omicron wave.

This result, released in Australia’s most recent serosurvey of antibodies to the virus in blood donors, is double the reported cases for the end of February, 2022.

The serosurvey was conducted by the National Centre for Immunisation Research and Surveillance (NCIRS) at Kids Research, Sydney Children’s Hospitals Network and the Kirby Institute at UNSW Sydney, in collaboration with Australian Red Cross Lifeblood, Victorian Infectious Diseases Reference Laboratory and other research partners. 

Researchers examined 5,185 de-identified samples from Australian blood donors aged 18–89 years for evidence of COVID-19–related antibodies in late February to early March 2022, about six weeks after the peak of the Omicron wave in NSW, the ACT, Queensland and Victoria.

Adults aged 18–29 years were found to have had the highest proportion of antibodies to SARS-CoV-2, at 27.2 per cent. This number then declined with increasing age to 6.4 per cent in the 70–89 years age group across NSW, Victoria and Queensland.

The survey also revealed Queensland had the highest antibody positivity rate at 26 per cent, followed by Victoria at 23 per cent, NSW at 21 per cent, while Western Australia had the lowest at 0.5 per cent.

Read more on the NCIRS website.