Poster Presentation Lorne Infection and Immunity 2022

Charting elimination in the pandemic: a SARS-CoV-2 serosurvey of blood donors in New Zealand (#117)

Lauren H. Carlton 1 , Tiffany Chen 1 , Alana L. Whitcombe 1 , Reuben McGregor 1 , Greg Scheurich 2 , Campbell R. Sheen 3 , James M. Dickson 4 , Chris Bullen 5 , Annie Chiang 5 , Daniel J. Exeter 5 , Janine Paynter 5 , Michael G. Baker 6 , Richard Charlewood 2 , Nicole J. Moreland 1
  1. School of Medical Sciences, The University of Auckland, Auckland, New Zealand
  2. The New Zealand Blood Service, Auckland, New Zealand
  3. Callaghan Innovation, Christchurch, New Zealand
  4. School of Biological Sciences, The University of Auckland, Auckland, New Zealand
  5. School of Population Health, The University of Auckland, Auckland, New Zealand
  6. Department of Public Health, University of Otago, Wellington, New Zealand

New Zealand had a strategy of eliminating SARS-CoV-2 that resulted in a low incidence of reported coronavirus-19 disease (COVID-19). The aim of this study was to describe the spread of SARS-CoV-2 in New Zealand via a nationwide serosurvey of blood donors, prior to vaccination roll-out. Samples (n=9806) were collected over a month-long period (December 3rd, 2020 - January 6th, 2021) from donors aged 16-88 years. The sample population was geographically spread, covering 16 of 20 district health board regions. A series of Spike-based immunoassays were utilized, and the serological testing algorithm was optimized for specificity given New Zealand is a low prevalence setting. Samples were first screened with a widely used and well‑validated 2‑step ELISA that comprises a single point dilution assay against the RBD followed by titration against trimeric S protein. Samples above the cut‑off were tested on two further immunoassays – the EuroImmun SARS‑CoV-2 IgG ELISA and the cPass surrogate Viral Neutralization Test and deemed seropositive if above the cut-off on both commercial assays. Of the 9806 samples, eighteen were seropositive for SARS-CoV-2 antibodies, six of which were retrospectively matched to previously confirmed COVID-19 cases. A further four were from donors that travelled to settings with a high risk of SARS-CoV-2 exposure, suggesting likely infection outside New Zealand.  The remaining eight seropositive samples were from seven different district health regions for a true seroprevalence estimate, adjusted for test sensitivity and specificity, of 0.103% (95% confidence interval, 0.09-0.12%).  The very low seroprevalence is consistent with limited undetected community transmission, providing robust, serological evidence to support New Zealand’s successful elimination strategy for COVID-19 prior to the emergence of the delta variant in the community in August 2021. This study also demonstrates the ability for blood donor services to be used to rapidly conduct seroprevalence studies, and highlights the ongoing need for vaccine-induced protection in the New Zealand population.