Seroprevalence of Severe Acute Respiratory Syndrome Coronavirus 2-Specific Antibodies in Australia After the First Epidemic Wave in 2020: A National Survey

Abstract

Background As of mid-2021, Australia’s only nation-wide COVID-19 epidemic occurred in the first six months of the pandemic. Subsequently there has been limited transmission in most states and territories. Understanding community spread during the first wave was hampered by initial limitations on testing and surveillance. To characterize the prevalence of SARS-CoV-2-specific antibody seroprevalence generated during this time, we undertook Australia’s largest national SARS-CoV-2 serosurvey. Methods Between 19 June-6 August 2020, residual specimens were sampled from people undergoing general pathology testing (all ages), women attending antenatal screening (20–39 years) and blood-donors (20–69 years) based on the Australian population’s age and geographic distributions. Specimens were tested by Wantai total SARS-CoV-2-antibody assay. Seroprevalence estimates adjusted for test performance were produced. SARS-CoV-2 antibody-positive specimens were characterized with microneutralization assays. Results Of 11,317 specimens (5132 general pathology; 2972 antenatal; 3213 blood-donors), 71 were positive for SARS-CoV-2-specific antibodies. Seroprevalence estimates were 0.47% (95% credible interval: 0.04-0.89%), 0.25% (0.03-0.54%) and 0.23% (0.04-0.54%), respectively. No seropositive specimens had neutralizing antibodies. Conclusions Australia’s seroprevalence was extremely low (<0.5%) following the only national COVID-19 wave thus far. These data and the subsequent limited community transmission highlight the population’s naivety to SARS-CoV-2 and the urgency of increasing vaccine-derived protection.

Serological testing of blood donors to characterise the impact of COVID-19 in Melbourne, Australia, 2020

“…Procedures followed those established for Australia’s first national COVID-19 serosurvey [ 5 ]. In Victoria, all blood donations are processed by Australian Red Cross Lifeblood (Lifeblood) through a single processing centre in Melbourne.…”

“…Specimens were tested at the Victorian Infectious Disease Reference Laboratory (Melbourne, Australia), using the Wantai SARS-CoV-2 total antibody enzyme-linked immunosorbent assay (ELISA; Beijing Wantai Biological Pharmacy Enterprise Co Ltd, China). We selected this assay based on in-house validations [ 5 ], including head-to-head comparisons of available commercial tests [ 8 ]. As previously described [ 5 ], we assessed Wantai performance on 102 stored specimens that were confirmed RT-PCR positive and collected more than 14 days post-symptom onset (median = 31 days, IQR = 21–40, max = 130).…”

“…We selected this assay based on in-house validations [ 5 ], including head-to-head comparisons of available commercial tests [ 8 ]. As previously described [ 5 ], we assessed Wantai performance on 102 stored specimens that were confirmed RT-PCR positive and collected more than 14 days post-symptom onset (median = 31 days, IQR = 21–40, max = 130). A positive result was found in 97, giving a test sensitivity of 97/102 = 95.1% (95% confidence interval: 88.9–98.4).…”

Serological Testing of Blood Donors to Characterise the Impact of Covid-19 in Melbourne, Australia, 2020

“…A positive result was found in 97, giving a test sensitivity of 97/102 = 95.1% (95% confidence interval: 88.9–98.4). We tested 800 (pre-pandemic) blood donor specimens from May 2019 and found three positive, giving a test specificity of 797/800 = 99.6% (98.9–99.9) [5].…”

“…Population surveys of SARS-CoV-2 antibody prevalence (serosurveys) can provide a better understanding of the cumulative prevalence of past infection and associated patterns. Surveys conducted in mid-2020 after Australia’s first wave used residual blood specimens from blood donors, pregnant women and people undergoing outpatient pathology testing [5, 6]. They found very low infection levels during the first COVID-19 epidemic wave, with the three populations providing similar results.…”