COVID rate at least double official figures: Antibody study

The results of an extensive antibody survey from blood donors across four Australian states have offered the most extensive evidence yet of how far official COVID figures differ from reality.
 
The serosurvey, conducted by the National Centre for Immunisation 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 reported positive cases.
 
Authors of a report released this week also state there are likely to be cases that have gone undetected even within the cohort they have looked at.
 
Researchers looked at 5185 Australian blood donor specimens taken from adults aged 18 and over, testing the prevalence of two separate types of antibodies. The first ‘anti-spike’ antibody is generated both by vaccines and infections and was found in 98% of those surveyed.
 
The rate does not vary much across areas, age groups or sex, and is higher than the overall vaccination rate. The authors suggest this could be the result of blood donors being 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 exists largely as a result of prior infection and can still be detected from 3–6 months after infection took place.
 
One of the more surprising findings from the survey is the higher rate of seroprevalence for this antibody among those tested in Queensland, which had the most extensive overall rate at 26% despite keeping its borders closed longer than other east coast states, following by Victoria (23%) and NSW (21%).  
 
The overall rate is 17%, with the highest rate among younger adults and the lowest among the elderly. Among those aged 70–89 years, the antibody showed up in just 6% of those tested.
 
Western Australia had the lowest level at all at 0.5%, having been at the very early stages of infection spread at the time of the study, with specimens taken from blood donations received between 23 February and 3 March 2022.
 
Dr Dorothy Machalek, the lead investigator on the project from the Kirby Institute, said the results correspond to expectations of much higher numbers due to asymptomatic infections, unreported results and symptomatic people who did not get tested.  
 
‘We’ve known from the start of the pandemic that using estimates of infection based on routine testing will always underestimate the number of infections in the community,’ she told newsGP.  
 
‘Certainly, it was no surprise that the number of infections based on our seroprevalence results was greater than the reported cases.’
 
The figures established from the survey are themselves also likely to be an underestimate of the true picture of the spread of the infection, the reports’ authors say.
 
Dr Machalek points to several potential reasons, including that the anti-nucleocapsid protein antibody fades so prior infection is unlikely to be picked among those who had COVID-19 earlier in the pandemic. The study estimates that more than one in five infections may be missed for this reason.
 
The authors also point to typical blood donor characteristics as a potential confounding factor.
 
‘It is well recognised that blood donors have a higher average income and education level and are healthier than the general population,’ they wrote. ‘These factors have been shown to impact health-seeking behaviour, including being associated with higher uptake of COVID-19 vaccination.’
 
The research helps to flesh out authorities’ understanding of the virus, according to Dr Machalek, who says it could influence healthcare planning.
 
‘It is really important to understand the spread of the infections, how widespread the virus is, where is it in the community, and how many people have been infected,’ she said.
 
‘It helps us with our pandemic planning for the future. We can understand what happened in the recent past, and we can understand how many people we identified as being infected versus how many people were actually infected.
 
‘We can then prepare for future waves and the potential impacts of those on hospitalisations and deaths. I think we can be much better prepared in the future, so it is still incredibly important.’
 
In the survey, Australia is shown as having a lower level of antibodies in the community compared to other countries.
 
However, Professor Kristine Macartney, director of the NCIRS, told Nine Newspapers the differences are likely to shrink.
 
‘Studies in the US and UK show the rate of antibodies is very steadily climbing,’ she said.
 
‘We are certainly under 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 the research relating to the situation more than three months ago, Dr Machalek is hopeful that more up-to-date detail will soon emerge to paint a fuller picture.
 
The results of an NCIRS study of paediatric COVID-19 infections are expected to be made public shortly, while work is ongoing on an analysis of the current situation, with the results hoped for by the end of July.
 
‘That’ll provide us a snapshot in time for what’s happening right now,’ Dr Machalek said.
 
‘We’ve had a couple of new variants come through, Western Australia has also had a massive spike in cases as well.’
 
Dr Machalek says a lag is inevitable given challenges in the way data is generated, analysed and made available.
 
‘It’s not like reporting daily case numbers,’ she said. ‘It’d be great to have that in real time, but it just doesn’t work like that, there’s always a bit of a delay.’
 
As for the implications of higher actual cases than the official count, Dr Machalek stresses the focus needs to be on the most at risk.
 
‘We are living in a time where we’re learning to live with the virus in many ways, so we’re seeing infection levels go up in the community,’ she said.
 
‘I think it does emphasise that we need to make sure that our most vulnerable sectors of the community are vaccinated and receive their boosters because it is going to be harder for people to avoid getting infected.’
 
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