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Vast majority of Australian population has had COVID: Seroprevalence survey
Upwards of eight in 10 people have at some point likely contracted the disease, which is now the third leading cause of death nationwide.
Kobie, age 11, having a blood test at The Children’s Hospital at Westmead as part of the seroprevalence survey. (Image: Supplied)
Official case numbers continue to greatly underestimate the spread of COVID-19 in the community, newly released seroprevalence survey results suggest.
Produced by the National Centre for Immunisation Research and Surveillance (NCIRS) and the Kirby Institute, the research indicates that at least 65% of adults in Australia had been infected with SARS-CoV-2 by the end of August 2022.
This proportion represented a jump of about 20% since the previous survey three months ago, showing that at least a fifth of the population had been exposed to the virus in that time period.
However, the researchers also say COVID’s true cumulative prevalence is likely to be even higher, as 15–20% of infections ‘may be missed by these seroprevalence estimates’.
Two types of antibodies were tested as part of the research: antibody to the nucleocapsid protein of the virus, which indicates past infection, and antibody to the spike protein, which can indicate past infection and/or vaccination.
A separate children and adolescents seroprevalence survey also found that at least 64% of 0–19-year-olds in Australia have been infected with SARS-CoV-2 – although the researchers again suggest this figure underestimates the true scale of transmission.
‘While spike antibodies were universally detected in vaccinated individuals, as expected, 65% of vaccinated individuals also had nucleocapsid antibodies, signifying past infection,’ the authors wrote.
‘At least 38% of children whose parents reported they had not previously been infected had evidence of infection due to the presence of nucleocapsid antibodies, suggesting asymptomatic or mild infection that may have been unrecognised.
‘In all children, the true cumulative SARS-CoV-2 infection rate is likely to be higher than that indicated by nucleocapsid seroprevalence, as data suggest that the sensitivity to detect nucleocapsid antibodies in vaccinated adults with breakthrough Omicron infections is around 84%.’
Evidence also suggests that nucleocapsid antibodies are produced at lower levels and wane faster in people who acquire infection following vaccination than those who have not been vaccinated, further reducing the sensitivity of nucleocapsid antibody assays in detecting previous infection.
At least four in five unvaccinated children showed signs of previous infection, while teenagers aged 16–17 showed the highest prevalence of nucleocapsid antibodies at 83%.
The surveys were released around the same time as the latest monthly COVID-19 mortality assessment report from the Actuaries Institute, which found excess mortality was 14% higher for the first seven months of 2022, equivalent to 13,700 deaths.
More than half of these deaths (7070) were attributed directly to COVID-19 – including 123 due to long COVID – while a further 1696 people had the disease listed as a contributory cause of death.
The ‘excess deaths’ due to causes other than COVID-19 include:
- ischaemic heart disease (1200 more deaths than expected)
- cerebrovascular disease (450 more)
- diabetes (400 more)
- dementia (800 more)
- doctor-certified deaths due to causes not specified by the ABS (2800 more)
- coroner-referred deaths (800 more).
A release from the Institute states that there are multiple factors potentially causing the ‘non-COVID-19’ excess deaths over this period, including:
- post-COVID-19 sequelae (conditions arising from COVID)
- delayed deaths from other causes
- delays in emergency care
- delays in routine care
- increased use of drugs and alcohol.
Karen Cutter, a spokesperson for the Institute’s COVID-19 Mortality Working Group, said it is not possible to identify from the data whether ‘any or all of these issues’ are causing the non-COVID-19 excess deaths.
However,
like previous reports, the Institute says post-COVID-19 sequelae has likely had a ‘high’ impact on this category.
Approximately 13,350 COVID-19 deaths have been recorded by state and territory health departments in the first 10 months of 2022, but the Institute estimates this includes 3550 people who died ‘with COVID’.
Nonetheless, the estimated 9800 deaths still leave COVID as the predicted third leading cause of death for 2022, behind dementia and ischaemic heart diseases.
And while Australia’s death rate was the
lowest on record in 2020, the trend has now reversed substantially. So far, all but one week of 2022 has been above the 97.5th percentile in terms of excess deaths.
It may also get worse in coming months, as New South Wales Chief Health Officer Dr Kerry Chant has joined her Victorian counterpart by issuing a warning about an
impending COVID wave fuelled by the XBB and BQ.1 Omicron subvariants.
‘We’re starting to see an increase in COVID cases and changes in the variants circulating in New South Wales, which tells us that we’re entering the next COVID wave,’ she said.
‘By looking at all the local information we have and what’s happening overseas, we believe COVID cases will rise in the coming weeks.
‘Make sure you’re up to date with your vaccinations. This is your best protection, including against the latest variants.’
Both XBB and BQ.1 have shown an ability to evade immunity conferred from previous infection and vaccination, although protection against severe disease is likely to remain strong – particularly for those who have received recent booster doses.
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