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ABC News
ABC News
national medical reporter Sophie Scott

Almost two-thirds of Australians — including children — have had COVID-19, blood study suggests

New research suggests almost two-thirds of Australians — including children and adolescents — have now had COVID-19 with authorities warning Australia is about to enter "the next COVID-19 wave". 

Australia's National Centre for Immunisation Research and Surveillance (NCIRS) tests blood samples from adults and children for COVID-19 antibodies every 13 weeks.

The most recent samples — collected between June and August this year — showed at least 65 per cent of Australian adults and 64 per cent of children had been infected with SARS-CoV-2 recently, likely in the past year.

That's a nearly-20-per-cent jump on the 46 per cent of infected adults from the last round of results published in June, and a massive increase from the 17 per cent of adults from results released in February.

On the most recent samples returned by children, NCIRS infectious diseases specialist Archana Koirala said this was "more than double the number of cases reported, based on nose and throat swab testing for the virus".

"This is expected, since many children have either mild or no symptoms and are, therefore, not tested for the virus," Dr Koirala said.

"By looking at vaccination status and history of infection in our study, we found four-out-of-10 children with no reported history of COVID-19 in fact were positive for antibodies, indicating [prior] infection."

The research showed unvaccinated children and teenagers had higher rates of infection than those who were vaccinated, with 82 per cent antibody rates in those aged birth to 19 years.

In other words, four-out-of-five unvaccinated children had been infected at some point.

However, in vaccinated children, antibodies were detected in 64 per cent of cases, with the highest rates seen in teenagers (70 per cent) and lower rates in children aged 1-4 years (61 per cent).

The rates of COVID-19 infections were similar between girls and boys, and also between Aboriginal and Torres Strait Islander and non-Indigenous children.

Official numbers show that 10.4 million COVID-19 cases have been reported in Australia. Those numbers include multiple infections, meaning the official reported figures across Australia's population of about 26 million are well below what this latest research suggests.

According to the NCIRS blood samples, the highest prevalence of antibodies was in the 18 to 29-year-old age group, with a massive 80 per cent testing positive.

They also showed there were 2.6 million new cases of COVID-19 reported in the Australian population between June and September 2022, with the Omicron BA.4 and BA.5 being the dominant variants.

The findings came from two sources: one survey of adult blood donors, and a second survey of children and adolescents undergoing an anaesthetic in hospital who were asked if they would give blood for medical research.

That research has shown the incidence of COVID-19 was spread evenly across all Australian states and territories.

GPs bracing for new COVID-19 wave

Last week, Victorian authorities reported a 25 per cent jump in COVID-19 numbers, while GPs in New South Wales are also being warned that case numbers are likely to rise.

An email sent to New South Wales GPs from primary health networks urged doctors to "prepare for an increase in local COVID-19 cases" and to "ensure patients are up to date with COVID-19 vaccinations".

In a video released on Thursday morning, NSW Chief Health Minister Kerry Chant said the state was "entering the next COVID-19 wave" and it was "likely" cases would rise in the coming weeks. 

While the Omicron strains BA.4 and BA.5 continue to be the most-common variants in Australia, their dominance is waning and new variants — such as XBB and BQ1.1 — are now circulating, according to New South Wales health authorities.

It's not completely clear how effective antiviral medications are to these newer variants.

After the increase in cases, epidemiologist Catherine Bennett told the ABC people should consider how they can reduce their risk of catching the virus.

"This isn't about saying: 'Oh no, now you have to panic again'," Professor Bennett said.

"This is about how we ride these waves in a way that allows us to moderate our behaviour appropriately."

Professor Bennett said that could involve wearing masks on transport and socialising outdoors, particularly around vulnerable people.

Mutations in the COVID-19 virus continue to pose a risk.
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