Thousands of blood samples will be routinely tested for COVID-19 antibodies under a planned national surveillance program that is set to reveal the extent of undetected virus across the population.
Experts anticipate the first survey results, to be released within weeks, could find a huge number of Omicron cases have gone undiagnosed, with estimates actual infections could be five to 10 times what was reported during the initial wave.
The first survey will examine about 5000 de-identified blood samples of donors across all jurisdictions.Credit:Brook Mitchell
“Until now we have relied mainly on PCR and rapid antigen testing to know how many people have been infected with the virus,” Kristine Macartney, project co-lead the director of the National Centre for Immunisation Research and Surveillance (NCIRS), said. “But checking blood samples for antibodies we can get a better snapshot of the missed cases and how much virus has been circulating in the community.”
“We also know many people are asymptomatic or perhaps didn’t get tested when they had the virus,” she said. “We’ve largely underestimated the true number of people infected with the virus. It is likely considerably higher than our virus testing data has told us.”
The first survey will examine about 5000 de-identified blood samples of donors across all jurisdictions, taken about six weeks after the Omicron peak. The population-level antibody studies, or serological surveys, are expected to run every three months.
Similar programs have run in the United Kingdom and United States, with the Office of National Statistics program testing thousands of people randomly in households across the UK during the pandemic.
Kirby Institute epidemiologist and project co-lead Dorothy Machalek said serology data was “vital because it provides a measure of COVID-19 infection in the context of a backdrop of a highly vaccinated population”.
It will also give us an idea of how states coped with the Omicron wave, largely without tough restrictions.
Dr Machalek said investigators will examine blood samples by age, sex and geographic location, which will “help us understand what variation there across the population”.
The serological surveys will be led by the NCIRS, UNSW’s Kirby Institute, Victorian Infectious Diseases Reference Laboratory at the Doherty Institute, Australian Red Cross Lifeblood, NSW Health Pathology’s Institute of Clinical Pathology and Medical Research and Murdoch Children’s Research Institute.
Investigators will test for different types of antibodies to estimate both the extent that the virus had spread in the community and the proportion of the population who have some levels of immunity, either through infection or vaccination.
They will look for a part of the virus called the nucleocapsid, which is only present in someone who has been infected with COVID-19, and for spike antibodies, which are produced by both natural infection and vaccination.
The surveys will help health authorities plan for rising cases of Omicron’s BA.2 sub-variant, vaccination, understanding how susceptible the population is and planning for hospital capacity in the case of subsequent waves.
NSW reported 20,087 cases on Thursday.
“Samples in the first survey were collected six weeks after the Omicron peak, which is sufficient for antibodies to have developed in people who were infected during that time,” said Professor Macartney. “This, along with regular future surveys including another planned in children, will mean we will be able to track the impact of changes in the COVID-19 response to better inform health policy.”
There have been four previous large-scale serosurveys in Australia, all conducted in 2020, that aimed to understand the level of community transmission and the impact of the restrictions. All surveys looked for antibodies in residual blood samples and donor blood.
All showed low infection levels, which provided strong evidence that COVID-19 transmission was limited in the first year of the pandemic.
Dr Machalek said as Omicron infections surged in December and January, the testing system collapsed, which meant many infections likely went undetected.
“We are expecting the results of the first survey to show infections are very high, much higher than in the first wave. Until the emergence of Omicron we thought we had a lot of cases, but we didn’t. And we had widely available testing,” she said.
“Blood donors make up around 3 per cent of the population. Although they cannot be viewed as a random sample of the population, they provide a stable and accessible pool from which to analyse infection prevalence over time,” Dr Machalek said.
The blood donation samples will be collected from Lifeblood’s blood processing centres across the country. Individual results will not be provided to blood donors.
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