The survey examined 5185 de-identified samples from Australian blood donors aged 18 to 89 to find evidence of COVID-19–related antibodies. Two types of antibody to SARS-CoV-2 were tested:the nucleocapsid protein,which is only present in someone who has been infected with COVID-19,and spike antibodies,which are produced by both natural infection and vaccination.
The highest proportion of adults with antibodies was in Queensland,where 26 per cent were shown to have had a COVID-19 infection by the end of February,despite only 10 per cent of Queenslanders having registered a test.
Twenty-three per cent of Victorian samples and 21 per cent of NSW samples showed antibodies gained by a prior infection. Western Australia was the outlier,with only 0.5 per cent of samples suggesting a prior case,as the state kept its borders shut until early March.
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“This is the first in a series of four planned serosurveys throughout the year,and is an important opportunity to better understand the characteristics of the virus and the dynamics of the pandemic,” John Kaldor from UNSW’s Kirby Institute said.
“We found evidence of recent infection in roughly twice the proportion of the population that had recorded infections in first major Omicron wave. We expect the true number to be even higher because the serology doesn’t detect every case.”
Professor Kristine Macartney,director of the NCIRS,said the results were expected,noting Australia had lower rates of antibodies in the community than similar surveys had found abroad.