Abstract
New Zealand has a strategy of eliminating SARS-CoV-2 that has 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. Samples (n = 9806) were collected over a month-long period (3 December 2020-6 January 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 utilised, and the serological testing algorithm was optimised for specificity given New Zealand is a low prevalence setting. Eighteen samples 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 and provides robust, serological evidence to support New Zealand's successful elimination strategy for COVID-19.
Highlights
Samples were collected by the New Zealand Blood Service via nine static collection centres and 36 mobile collection services over a 4-week period (3 December 2020–6 January 2021) from individuals aged 16–88 years
Priority ethnicity is reported as defined by the New Zealand Department of Statistics. a‘Other’ comprises of n = 28 (0.20%) of the blood donor population, and n = 51 447 (1.10%) of the New Zealand census population. bAll blood donors are at least 16 years of age
Samples above the cut-off were tested on two further immunoassays – the EuroImmun SARS-CoV-2 IgG ELISA (EuroImmun AG, Lübeck, Germany) and the cPass surrogate Viral Neutralisation Test (GenScript, New Jersey, USA) and the values deemed seropositive if above the cut-off on both commercial assays
Summary
Samples were collected by the New Zealand Blood Service via nine static collection centres and 36 mobile collection services over a 4-week period (3 December 2020–6 January 2021) from individuals aged 16–88 years. The New Zealand blood service donations were collected between the 3rd of December 2020 and the 6th of January 2021. Notable travel and a history SARS-CoV-2 infection (or contact with a positive case) are recorded prior to collection.
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