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At least 17% of Australians may have contracted COVID-19 during the first Omicron wave, according to new research – and the true figure could be even higher.
New information on the prevalence of COVID-19 has been extracted from blood donor records.
The results of a large antibody survey of blood donors in four Australian states have offered the most comprehensive evidence yet of the difference between official COVID numbers and reality.
The serological survey, conducted by the National Center for Immunization Research and Surveillance (NCIRS) and the Kirby Institute at UNSW Sydney, indicates that the number of people who have had COVID-19 is at least double the official number of positive cases reported.
The authors of a report published this week also say that cases are likely to go undetected, even within the cohort they examined.
The researchers looked at 5,185 Australian blood donor samples taken from adults aged 18 and over, testing for the prevalence of two distinct types of antibodies. The first “anti-spike” antibody is generated by both vaccines and infections and was found in 98% of those surveyed.
The rate does not vary much by area, age group or sex, and is higher than the overall vaccination rate. The authors suggest this could be because blood donors are more likely to be vaccinated than the population as a whole.
They also tested for the presence of a second anti-nucleocapsid protein antibody, which largely exists as a result of previous infection and can still be detected 3-6 months after infection.
One of the most surprising findings from the survey is the higher seroprevalence rate for this antibody among those tested in Queensland, which had the most widespread overall rate at 26% despite keeping its borders closed longer than the other east coast states, followed by Victoria (23%) and New South Wales (21%).
The overall rate is 17%, highest among young adults and lowest among the elderly. Among people aged 70 to 89, the antibody only appeared in 6% of those tested.
Western Australia had the lowest level at all at 0.5%, having been in the very early stages of the spread of the infection at the time of the study, with samples taken from blood donations received between February 23 and March 3, 2022.
Dr. Dorothy Machalek, principal investigator of the Kirby Institute project, said the results match expectations of much higher numbers due to asymptomatic infections, unreported results and symptomatic people who have not been tested. .
“We have known since the start of the pandemic that using infection estimates based on routine testing will always underestimate the number of infections in the community,” she said. newsGP.
“It is certainly not surprising that the number of infections based on our seroprevalence results is higher than the reported cases.”
The figures drawn from the survey are themselves likely to underestimate the true picture of the spread of the infection, according to the authors of the reports.
Dr. Machalek points to several potential reasons, including that the anti-nucleocapsid protein antibody fades, so that prior infection is unlikely to be detected among those who had COVID-19 earlier in life. pandemic. The study estimates that more than one in five infections may be missed for this reason.
The authors also point to typical characteristics of blood donors as a potential confounding factor.
“It is well recognized that blood donors have a higher average income and education level and are in better health than the general population,” they wrote. “These factors have been shown to impact healthcare-seeking behavior, including being associated with greater uptake of COVID-19 vaccination.”
The research is helping flesh out authorities’ understanding of the virus, according to Dr Machalek, who says it could influence health care planning.
“It’s really important to understand the spread of infections, the extent of the virus, where is it in the community and how many people have been infected,” she said.
“It helps us in our pandemic planning for the future. We can understand what has happened in the recent past, and we can understand how many people we have identified as infected versus how many people are actually infected.
“We can then prepare for future waves and the potential impacts of these on hospitalizations and deaths. I think we can be much better prepared for the future, so that’s still hugely important.
In the survey, Australia is shown to have a lower level of antibodies in the community compared to other countries.
However, Professor Kristine Macartney, director of the NCIRS, told Nine Newspapers that the differences are likely to narrow.
“Studies in the US and UK show that antibody levels are rising very steadily,” she said.
“We are certainly below that proportion, but we suspect that over time, as the virus continues to circulate and we have limited restrictions, we will reach those levels.”
With research relating to the situation more than three months ago, Dr Machalek hopes more up-to-date details will emerge soon to paint a fuller picture.
The results of an NCIRS study of pediatric COVID-19 infections are expected to be made public shortly, while work is underway on an analysis of the current situation, with results expected by the end of July.
“It will give us an in-time snapshot of what’s happening right now,” Dr Machalek said.
“We’ve had a few new variants, Western Australia has also seen a massive increase in cases.”
Dr Machalek says a lag is inevitable given the difficulties in how data is generated, analyzed and made available.
“It’s not like reporting daily case numbers,” she said. “It would be nice to have that in real time, but it doesn’t work like that, there’s always a bit of a delay.”
As for the implications of actual cases higher than the official tally, Dr Machalek stresses that the focus must be on those most at risk.
“We live in a time where we are learning to live with the virus in many ways, so we are seeing infection levels rise in the community,” she said.
“I think it underscores that we need to make sure our most vulnerable sectors of the community are vaccinated and get their booster shots because it will be harder for people to avoid getting infected.”
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