Aussie COVID-19 cases higher than reported

By the end of February 2022, it was estimated that at least 17% of Australia’s adult population had been recently infected with SARS-CoV-2, the virus that causes COVID-19, according to the results of Australia’s most recent antibody seroscan for the virus in blood donors released today . The vast majority of these infections are believed to have occurred during the Omicron wave, which began in December 2021. Based on survey results, the proportion of people infected was at least double the cases reported to authorities by the end of February 2022.

The seroassay was conducted by the National Center for Immunization Research and Surveillance (NCIRS) and the Kirby Institute at UNSW Sydney in collaboration with the Australian Red Cross Lifeblood, the Victorian Infectious Diseases Reference Laboratory and other research partners.

The highest proportion of adults with antibodies to SARS-CoV-2 was in Queensland (26%), followed by Victoria (23%) and New South Wales (21%), while Western Australia had the lowest proportion (0.5%). .

The Serosurvey method detects higher rates of infection than routine surveillance based on cases diagnosed and reported at the time of infection, which overlooks people who did not show up for a test or whose positive test result was not reported to authorities.

The national antibody survey was conducted in late February-early March 2022, approximately 6 weeks after the peak of the Omicron wave in New South Wales, the Australian Capital Territory, Queensland and Victoria and prior to significant transmission in Western Australia.

“The overall pattern of antibody positivity in blood donors was consistent with the pattern in reported cases up to the end of February 2022: New South Wales, Victoria and Queensland had large outbreaks and Western Australia had very limited community transmission,” says Dr. Dorothy Machalek, lead investigator on the project from the Kirby Institute. “Similarly, young blood donors had the highest infection rate, consistent with higher reported case numbers in this age group.”

The researchers examined 5,185 de-identified samples from Australian blood donors aged 18 to 89 for evidence of COVID-19-related antibodies. Two types of antibodies against SAR-CoV-2 have been tested: antibodies against the nucleocapsid protein, which provides an indication of previous infection, and antibodies against the spike protein, which can indicate previous infection and/or vaccination.

Evidence of prior infection was highest in donors aged 18-29 years at 27.2% and decreased with age to 6.4% in donors aged 70-89 years in Victoria, New South Wales and Queensland . In Western Australia, evidence of recent infection was extremely low across all age groups. Nationwide, the proportion of the population with antibodies against the spike protein was much higher at around 98%.

“As expected, a very high proportion of blood donors had antibodies against the spike protein of the COVID-19 virus, with small variations by age group and gender. This was probably due to the high vaccination rates among blood donors as well as among the wider population,” says Professor Kristine Macartney, Director of NCIRS and Professor at the University of Sydney.

“Future rounds of the blood donor serosurvey will allow us to understand how many infections will occur in 2022,” Professor Macartney said. “We are also conducting a second national pediatric serosurvey, which began collecting in June, and this will give us better insight into transmission in children and adolescents.”

The ongoing blood donor survey, conducted jointly by the Kirby Institute and NCIRS in collaboration with the Australian Red Cross Lifeblood, also involves investigators from the Victorian Infectious Diseases Reference Laboratory at the Doherty Institute, NSW Health Pathology ICPMR, the University of Sydney and Murdoch Children’s Research Institute .

The remaining blood donation samples used in the survey were obtained from Lifeblood’s processing centers across the country and stripped of all identifying information except for age, gender and zip code. Individual results can therefore not be returned to blood donors.

“Australian Red Cross Lifeblood encourages anyone who wishes to contribute to this type of research to become a regular donor. There are many benefits to making a donation, including getting your blood type checked,” says Professor David Irving, Director of Research and Development at the Australian Red Cross Lifeblood.

The next round of the Lifeblood donor survey started in mid-June. At this time, the prevalence of SARS-CoV-2 antibodies is estimated after the spread of Omicron BA.2 and other subvariants. The data will be made available to all states, territories and the Commonwealth government as part of the Australian National Disease Surveillance Plan for COVID-19.

Provided by the Kirby Institute for Infection and Immunity in Society