ABSTRACT
A large-scale SARS-CoV-2 serosurvey of New Zealand blood donors (n=9806) was conducted at the end of 2020. Seroprevalence, after adjusting for test sensitivity and specificity, was very low (0.1%). This finding is consistent with limited community transmission and provides robust evidence to support New Zealand s successful elimination strategy for COVID-19.
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.
