ABSTRACT
During the first wave of SARS-CoV-2 infection in New Zealand a cohort of 78 PCR-confirmed COVID-19 cases was recruited in the Southern District Health Board region. Here we report on this unique cohort nearly 1-year after infection. There was no known community transmission in the region over the study period due to New Zealands elimination status at the time, nor had any participants received a COVID-19 vaccine. In the absence of re-exposure, antibody reactivity to the viral spike protein, as well as neutralising antibodies to both the ancestral strain and the delta variant remained relatively stable between 8 and 11 months post-infection. This suggests long-lived antibody responses can be generated from a single natural infection event. However, given the risks of serious disease associated with SARS-CoV-2 infection, vaccination is still strongly recommended.
ABSTRACT
ObjectivesCirculating antibodies are important markers of previous infection and immunity. Questions remain with respect to the durability and functionality of SARS-CoV-2 antibodies. This study explored antibody responses in recovered COVID-19 patients in a setting where the probability of re-exposure is effectively nil, owing to New Zealands successful elimination strategy. MethodsA triplex bead-based assay that detects antibody isotype (IgG, IgM and IgA) and subclass (IgG1, IgG2, IgG3, IgG4) responses against Nucleocapsid (N) protein, Receptor Binding Domain (RBD) and Spike (S) protein of SARS-CoV-2 was developed. After establishing baseline levels with pre-pandemic control sera (n=113), samples from PCR-confirmed COVID-19 patients with mild-moderate disease (n=189) collected up to eight months post-infection were examined. The relationship between antigen-specific antibodies and neutralising antibodies (NAbs) was explored with a surrogate neutralisation assay that quantifies inhibition of the RBD/hACE-2 interaction. ResultsWhile most individuals had broad isotype and subclass responses to each antigen shortly after infection, only RBD and S protein IgG, as well as NAbs, were stable over the study period, with 99%, 96% and 90% of samples, respectively, having responses over baseline 4-8 months post-infection. Anti-RBD antibodies were strongly correlated with NAbs at all time points (Pearsons r [≥] 0.87) and feasibility of using finger prick sampling to accurately measure anti-RBD IgG was demonstrated. ConclusionAntibodies to SARS-CoV-2 persist for up to eight months following mild to moderate infection. This robust response can be attributed to the initial exposure without immune boosting given the lack of community transmission in our setting.
ABSTRACT
BackgroundDuring New Zealands 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. ObjectivesTo evaluate the Abbott(R) 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 designPre-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. ResultsThe 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. ConclusionsSpike-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.
