ABSTRACT
Low-volume antibody assays can be used to track SARS-CoV-2 infection rates in settings where active testing for virus is limited and remote sampling is optimal. We developed 12 ELISAs detecting total or antibody isotypes to SARS-CoV-2 nucleocapsid, spike protein or its receptor binding domain (RBD), 3 anti-RBD isotype specific luciferase immunoprecipitation system (LIPS) assays and a novel Spike-RBD bridging LIPS total-antibody assay. We utilised pre-pandemic (n=984) and confirmed/suspected recent COVID-19 sera taken pre-vaccination rollout in 2020 (n=269). Assays measuring total antibody discriminated best between pre-pandemic and COVID-19 sera and were selected for diagnostic evaluation. In the blind evaluation, two of these assays (Spike Pan ELISA and Spike-RBD Bridging LIPS assay) demonstrated >97% specificity and >92% sensitivity for samples from COVID-19 patients taken >21 days post symptom onset or PCR test. These assays offered better sensitivity for the detection of COVID-19 cases than a commercial assay which requires 100-fold larger serum volumes. This study demonstrates that low-volume in-house antibody assays can provide good diagnostic performance, and highlights the importance of using well-characterised samples and controls for all stages of assay development and evaluation. These cost-effective assays may be particularly useful for seroprevalence studies in low and middle-income countries.
Subject(s)
COVID-19 , Myocardial Bridging , Mastocytosis, SystemicABSTRACT
Saliva is easily obtainable non-invasively and potentially suitable for detecting both current and previous SARS-CoV-2 infection. We established 6 standardised enzyme linked immunosorbent assays (ELISA) capable of detecting IgA and IgG antibodies to whole SARS-CoV-2 spike protein, to its receptor binding domain region and to nucleocapsid protein in saliva. In test accuracy (n=320), we found that spike IgG performed best (ROC AUC: 95.0%, 92.8-97.3%), followed by spike IgA (ROC AUC: 89.9%, 86.5-93.2%) for discriminating between pre-pandemic and post COVID-19 saliva samples. Using machine learning, diagnostic performance was improved when a combination of tests was used. As expected, salivary IgA was poorly correlated with serum, indicating an oral mucosal response whereas salivary IgG responses were predictive of those in serum. When deployed to 20 household outbreaks undergoing Delta and Omicron infection, antibody responses were heterogeneous but remained a reliable indicator of recent infection. Intriguingly, unvaccinated children showed evidence of exposure almost exclusively through specific IgA responses in the absence of evidence of viral infection. We have provided robust standardisation, evaluation, and field-testing of salivary antibody assays as tools for monitoring SARS-CoV-2 immune responses. Future work should focus on investigating salivary antibody responses following infection and vaccination to understand patterns of SARS-CoV-2 transmission and inform ongoing vaccination strategies.
Subject(s)
COVID-19 , Virus DiseasesABSTRACT
The SARS-CoV-2 virus causes COVID-19, an infection capable of causing severe disease and death but which may also be asymptomatic or oligosymptomatic in many individuals. While several risk factors, including age, have been described, the mechanisms of this variation are poorly understood. Several studies have described associations between blood group and COVID-19 severity, while others do not. Expression of ABO glycans on secreted proteins and non-erythroid cells is controlled by a fucosyltransferase (FUT2). Inactivating mutations result in a non-secretor phenotype which is known to protect against some viral infections. We investigated whether ABO or secretor status was associated with COVID-19 severity. Data combined from healthcare records and laboratory tests (n=275) of SARS-CoV-2 PCR positive patients hospitalised with COVID-19, confirmed higher than expected numbers of blood group A individuals compared to O (RR=1.24, CI 95% [1.05,1.47], P=0.0111). There was also a significant association between group A and COVID-19-related cardiovascular complications (RR=2.56, CI 95% [1.43,4.55], P=0.0011) which is independent of gender. Molecular analysis of phenotype revealed that group A patients who are non-secretors are significantly less likely to be hospitalised than secretors. In a larger cohort of 1000 convalescent plasma donors, among whom the majority displayed COVID-19 symptoms and only a small minority required hospitalisation, group A non-secretors were slightly over-represented. Our findings indicate that group A non-secretors are not resistant to infection by SARS-CoV-2, but they are likely to experience a less severe form of its associated disease. Key PointsO_LIBlood group type A is associated with an increased risk of cardiovascular complications in COVID-19 patients. C_LIO_LIFUT2 "non-secretor" status reduces the risk of severe COVID-19 outcomes in patients with blood group A. C_LI