SARS-CoV-2 antibodies in the Southern Region of New Zealand, 2020

Abstract

Background: During New Zealand's first outbreak in early 2020 the Southern Region had the highest per capita SARS-CoV-2 infection rate. PCR testing was initially limited by a narrow case definition and limited laboratory capacity, so cases may have been missed. Objectives: To evaluate the Abbott SARS-CoV-2 IgG nucleocapsid assay, alongside spike-based assays, and to determine the frequency of antibodies among PCR-confirmed and probable cases, contacts, and higher risk individuals in the Southern Region of NZ. Study design: Pre-pandemic sera (n=300) were used to establish assay specificity and sera from PCR-confirmed SARS-CoV-2 patients (n=78) to establish sensitivity. For prevalence analysis, all samples (n=1214) were tested on the Abbott assay, and all PCR-confirmed cases (n=78), probable cases (n=9), and higher risk individuals with grey-zone (n=14) or positive results (n=11) were tested on four additional SARS-CoV-2 serological assays. Results: The median time from infection onset to serum collection for PCR-confirmed cases was 14 weeks (range 11-17 weeks). The Abbott assay demonstrated a specificity of 99.7% (95% CI, 98.2%-99.99%) and a sensitivity of 76.9% (95% CI, 66.0%-85.7%). Spike-based assays demonstrated superior sensitivity ranging 89.7-94.9%. Nine previously undiagnosed sero-positive individuals were identified, and all had epidemiological risk factors. Conclusions: Spike-based assays demonstrated higher sensitivity than the Abbott IgG assay, likely due to temporal differences in antibody persistence. No unexpected SARS-CoV-2 infections were found in the Southern region of NZ, supporting the elimination status of the country at the time this study was conducted.

Comprehensive analysis of SARS-CoV-2 antibody dynamics in New Zealand

“…A triplex bead-based immunoassay was developed, with N protein, trimeric S protein and RBD coupled to spectrally unique beads. Compatibilty of the beads in a multiplex format was confirmed, as was comparability with previously described ELISA for S protein and RBD 22 , and N protein titres determined using the Abbott Architect SARS-CoV-2 IgG assay 23 , with highly significant correlations for all three antigens (Supplementary Figure 1). The level of SARS-CoV-2 antigen specific isotypes (IgG, IgM, IgA) and subclasses (IgG1, 2, 3 and 4) were determined in a cohort of 112 PCR-confirmed COVID-19 participants, 50 of whom had multiple time points (n=189 samples), and the majority of whom had mild disease (Table 1).…”

“…22 Samples from PCR-confirmed COVID-19 individuals were obtained from hospital in-patients in Auckland (n=18) (ethics HDEC 20NTB76) and convalescent participants in the Southern Region of New Zealand (ethics HDEC 20NTB101) as previously described. 22,23 Samples were also obtained from donors with a prior COVID-19 diagnosis, collected at the New Zealand Blood service as part of a Medsafe approved process for convalescent plasma preparation. The final PCR-confirmed cohort in this study comprised 189 samples from 112 participants, 50 of whom had samples collected at multiple time points (Table 1).…”

Comprehensive analysis of SARS‐CoV‐2 antibody dynamics in New Zealand

“…A triplex bead-based immunoassay was developed, with N protein, trimeric S protein and RBD coupled to spectrally unique beads. Compatibility of the beads in a multiplex format was confirmed, as was comparability with previously described ELISA for S protein and RBD, 22 and the N protein Abbott Architect SARS-CoV-2 IgG assay, 23 with highly significant correlations for all three antigens (Supplementary figure 1). The level of SARS-CoV-2 antigen-specific isotypes (IgG, IgM and IgA) and subclasses (IgG1, IgG2, IgG3 and IgG4) was determined in a cohort of 112 PCR-confirmed COVID-19 participants, 50 of whom had multiple time points (n = 189 samples), and the majority of whom had mild disease (Table 1, Supplementary figure 2).…”

“…Samples collected before the pandemic were used as negative controls (‘pre‐pandemic’, n = 113), details of which have been described previously 22 . Samples from PCR‐confirmed COVID‐19 individuals were obtained from hospital inpatients in Auckland ( n = 18) (ethics HDEC 20NTB76) and convalescent participants in the Southern Region of New Zealand (ethics HDEC 20NTB101) as previously described 22,23 . Samples were also obtained from donors with a prior COVID‐19 diagnosis, collected at the New Zealand Blood Service as part of a Medsafe‐approved process for convalescent plasma preparation.…”

“…22 Samples from PCR-confirmed COVID-19 individuals were obtained from hospital inpatients in Auckland (n = 18) (ethics HDEC 20NTB76) and convalescent participants in the Southern Region of New Zealand (ethics HDEC 20NTB101) as previously described. 22,23 Samples were also obtained from donors with a prior COVID-19 diagnosis, collected at the New Zealand Blood Service as part of a Medsafe-approved process for convalescent plasma preparation. The final PCRconfirmed cohort in this study comprised 189 samples from 112 participants, 50 of whom had samples collected at multiple time points (Table 1, Supplementary figure 2).…”