Blood samples with COVID-19 antibodies hold clues on rates of infected Australian children

By Melissa Coade

June 13, 2022

At least one in 500 children was infected with COVID-19 by the start of last year. (Quality Stock Arts/Adobe)

Researchers estimate at least one in 500 children was infected with COVID-19 by the start of last year, based on a review of ‘seroprevalence’ in elective surgery blood samples.

A new study published in the Medical Journal of Australia has estimated between 0.21% and 0.42% children (or more than 13,500 people) were infected with COVID-19 nationwide by early 2021.

The estimate was made using data extrapolated from elective surgery blood samples taken between November 2020 and March 2021. Researchers checked the samples, collected during anaesthesia, for evidence of COVID-19 antibodies known as ‘seroprevalence’. The findings were then extrapolated to the broader population of Australian children.

In a statement on Monday, the paper authors said seroprevalence measurement was an important way of understanding the fraction of a population that had contracted the virus. 

The two only other ways of understanding this number were data from positive RAT and PCR results during an active COVID infection. But this approach resulted in an undercount of infections because all infected people would not necessarily be tested or report their results. 

According to lead author Dr Archana Koirala, the consent-based, ‘opportunistic’ means of using blood samples to estimate seroprevalence was a useful approach. 

“Our [method] was highly effective in achieving the required sample size for analysis and could be used for future seroepidemiological monitoring of SARS-CoV-2 in children, especially after the surge in infections from mid-2021,” Koirala said. 

The paediatric infectious diseases physician from Nepean Hospital added the method could be used to track the spread of the virus as the pandemic continued. 

Of the blood samples examined, SARS-CoV-2-specific antibodies were detected in seven patients. One positive result was in a child aged 5-9 years, and another six positive results in six children aged 10-19 years.

“[There were] three in Victoria, three in New South Wales, and one in Queensland,” the researchers said.

“Three specimens were also positive in immunofluorescent antibody and microneutralisation assays.”

Based on the data findings, the researchers determined the base case prior distribution for Australians aged 0-19 years was 0.23%. This is equivalent to 13,719 people in the mainland states of Australia who were infected with COVID-19 by early 2021.

“Using a less conservative prior distribution (greater weight assigned to lower seroprevalence values), estimated seroprevalence was 0.16%, corresponding to 9,545 infections,” the paper added. 


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