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Tuesday, August 9, 2022

17 per cent of the Australian population estimated to have contracted Omicron variant: new study

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According to a new study of blood-donor samples, it is estimated that 17 per cent of the Australian adult population has recently been infected with the Omicron strain of COVID-19, giving a new meaning to being “O-positive”.

Conducted by the National Centre for Immunisation Research and Surveillance (NCIRS) and the Kirby Institute at UNSW Sydney, in collaboration with Australian Red Cross Lifeblood and the Victorian Infectious Diseases Reference Laboratory, the research indicates that the proportion of people infected was at least twice as high as indicated by cases reported to authorities by the end of February 2022.

However, Omicron infection rates in older Australians aged 70–89 were found to be proportionately lower than the average, at 6.4 per cent.

This new data comes as Prime Minister Anthony Albanese announced an extra $760 million to help the states and territories deal with COVID-19, extending federal government support until December 31, 2022.

As of the last federal health data report (June 17) there were 644 active COVID outbreaks in residential aged care facilities across the country, with 3316 residents currently battling an infection.

Dr Dorothy Machalek, lead investigator on the project from the Kirby Institute, said that her research project’s findings were consistent with state-by-state data.

“The general pattern of antibody positivity in blood donors was consistent with the pattern in reported cases to the end of February 2022: New South Wales, Victoria and Queensland having had big outbreaks, and Western Australia having very limited community transmission.”

The highest proportion of adults with antibodies to SARS-CoV-2 was in Queensland (26 per cent), followed by Victoria (23 per cent) and New South Wales (21 per cent), while Western Australia had the lowest (0.5 per cent).

Dr Dorothy Machalek, senior research fellow at the Kirby Institute, says that the sero-study tracked consistently with state governments’ data, however it indicated that a higher proportion of people have been infected with the Omicron strain than first thought.

The national antibody survey was conducted in late February to early March 2022, approximately 6 weeks after the peak of the Omicron wave in New South Wales, the Australian Capital Territory, Queensland and Victoria and prior to substantial transmission in Western Australia.

Researchers examined 5,185 de-identified samples from Australian blood donors aged 18–89 years for evidence of COVID-19–related antibodies.

Two types of antibody to SAR-CoV-2 were tested: antibody to the nucleocapsid protein, which provides an indication of past infection, and antibody to the spike protein, which can indicate past infection and/or vaccination.

Evidence of past infection in New South Wales, the Australian Capital Territory, Queensland and Victoria was highest among donors aged 18–29 years at 27.2 per cent, with infection rates declining with increasing age.

In Western Australia, evidence of recent infection was extremely low across all age groups.

Professor Kristine Macartney, Director of NCIRS, notes that, unsurprisingly, the proportion of the population with antibodies to the spike protein was far higher, at around 98 per cent.

“As expected a very high proportion of the blood donors had antibodies to the spike protein of the COVID-19 virus, with little variation by age group and sex,” she said.

“This was likely due to high vaccination rates among blood donors, as well as in the wider population.”

Professor Kristine Macartney, director of National Centre for Immunisation Research & Surveillance (NCIRS), says that high vaccination rates account for COVID antibody presence in 98 per cent of samples.

Macartney said that further studies will be conducted throughout this year to understand the ongoing spread of the virus, especially Omicron BA.2 and other subvariants.

“Future rounds of the blood donor sero-survey will allow us to understand how many infections occur throughout 2022.

“We are also conducting a second national paediatric sero-survey that started collection in June and this will give us better insights into transmission in children and teenagers.”

Professor David Irving, director of research and development at Australian Red Cross Lifeblood, said that blood donors, already saving lives, can now confer an added benefit to science by rolling up their sleeves.

“Australian Red Cross Lifeblood encourages anyone wanting to contribute to this type of research to become a regular donor,” he said.

The residual blood donation samples used in the surveys are obtained from Lifeblood’s processing centres across the country and delinked from any identifying information apart from age, sex and post code.

Individual results can therefore not be provided back to blood donors.

The next round of the Lifeblood donor survey has commenced from mid-June.

This time point will estimate SARS-CoV-2 antibody prevalence following the spread of the Data are provided to all states, territories and the Commonwealth Government under the Australian National Disease Surveillance Plan for COVID-19.

The National Centre for Immunisation Research and Surveillance (NCIRS) is the leading research organisation in Australia working to support evidence-based policy development for the National Immunisation Program and surveillance of vaccine preventable diseases, vaccine coverage and vaccine safety.

This work is funded through agreements with the federal health department.

The Kirby Institute is a world-leading health research organisation at UNSW Sydney working to eliminate infectious diseases, globally.

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