A dual antigen ELISA allows the assessment of SARS-CoV-2 antibody seroprevalence in a low transmission setting

Estimates of seroprevalence of SARS-CoV-2 antibodies have been hampered by inadequate assay sensitivity and specificity. Using an ELISA-based approach to that combines data about IgG responses to both the Nucleocapsid and Spike-receptor binding domain antigens, we show that near-optimal sensitivity and specificity can be achieved. We used this assay to assess the frequency of virus-specific antibodies in a cohort of elective surgery patients in Australia and estimated seroprevalence in Australia to be 0.28% (0 to 0.72%). These data confirm the low level of transmission of SARS-CoV-2 in Australia before July 2020 and validate the specificity of our assay. ### Competing Interest Statement NC is an employee of the Australian Government Department of Health and Ageing contributed to study design, interpretation of results, and approval of the manuscript. All other authors declare no competing interests. ### Funding Statement The study was sponsored by the Australian Government Department of Health and Ageing and Medibank Private. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Collection of blood from individuals pre-2020 was carried out after provision of informed consent, using procedures approved by the Human Research Ethics Committees (HREC) of the Australian National University (2016/317) and ACT Health (1.16.011 and 1.15.015). Samples from SARS-CoV-2 positive individuals were collected after consent under the following protocols: Alfred Hospital HREC (280/14); James Cook University HREC (#H7886); ACT Health HREC (1.16.011): Charite Ethics Committee (EA2/066/20) [7]. Approval for the elective surgery study was given by Alfred Hospital Ethics Committee (339/20) and the Australian National University (2020/379). All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data pertaining to this paper is reported in the manuscript.