Analysis of SARS-CoV-2 Ig seroprevalence in Northern Ireland

Background With the impact of SARS-CoV-2 upon public health directly and socioeconomically, further information was required to inform policy decisions designed to limit virus spread. This study sought to contribute to serosurveillance work within Northern Ireland to track SARS-CoV-2 progression and guide health strategy. Methods Sera/plasma samples from clinical biochemistry laboratories were analysed for anti-SARS-CoV-2 immunoglobulins (Ig). Samples were assessed using an Elecsys anti-SARS-CoV-2 or anti-SARS-CoV-2 S ECLIA (Roche) on an automated Cobas-e-analyser. Samples were also assessed via ELISA (Euroimmun). A subset of samples assessed via Roche Elecsys anti-SARS-CoV-2 IgG assay were subsequently analysed in an ACE2 pseudoneutralisation assay using a V-PLEX SARS-CoV-2 Panel 7 for IgG and ACE2 by MesoScale Diagnostics Inc. Results Across three testing rounds (June-July 2020, November-December 2020 and June-July 2021 (rounds 1-3 respectively)), 4844 residual sera/plasma specimens were assayed for SARS-CoV-2 Ig. Seropositivity rates increased across the study, peaking at 11.6% during round 3. Varying trends in SARS-CoV-2 seropositivity were noted based on demographic factors. For instance, highest rates of seropositivity shifted from older to younger demographics across the study period. In round 3, alpha (B.1.1.7) variant neutralising antibodies were most frequently detected across age groups, with median concentration of anti-spike protein antibodies elevated in 50-69 year olds and anti-S1 RBD antibodies elevated in over 70s, relative to other age groups. Conclusions With seropositivity rates of <15% across the assessment period, it can be concluded that the significant proportion of the Northern Ireland population had not yet naturally contracted the virus by mid-2021. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors ### 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: Ethical approval for this study was obtained from the Northern Ireland Biobank. The Northern Ireland Biobank has ethical approval from The Office of Research Ethics Committees Northern Ireland (ORECNI REF 21/NI/0019) and can confer ethical approval for projects which have received material from the bank I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. 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, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes