A cell-free high throughput assay for assessment of SARS-CoV-2 neutralizing antibodies.

Highly accurate serological tests are key to assessing the prevalence of SARS-CoV-2 antibodies and the level of immunity in the population. This is important to predict the current and future status of the pandemic. With the recent emergence of new and more infectious SARS-CoV-2 variants, assays allowing for high throughput analysis of antibodies able to neutralize SARS-CoV-2 become even more important. Here, we report the development and validation of a robust, high throughput method, which enables the assessment of antibodies inhibiting the binding between the SARS-CoV-2 spike protein and angiotensin converting enzyme 2 (ACE2). The assay uses recombinantly produced spike-f and ACE2 and is performed in a bead array format, which allows analysis of up to 384 samples in parallel per instrument over seven hours, demanding only one hour of manual handling. The method is compared to a microneutralization assay utilising live SARS-CoV-2 and is shown to deliver highly correlating data. Further, a comparison with a serological method that measures all antibodies recognizing the spike protein shows that this type of assessment provides important insights into the neutralizing efficiency of the antibodies, especially for individuals with low antibody levels. This method can be an important and valuable tool for large-scale assessment of antibody-based neutralization, including neutralization of new spike variants that might emerge.

Multianalyte serology in home-sampled blood enables an unbiased assessment of the immune response against SARS-CoV-2.

Serological testing is essential to curb the consequences of the COVID-19 pandemic. However, most assays are still limited to single analytes and samples collected within healthcare. Thus, we establish a multianalyte and multiplexed approach to reliably profile IgG and IgM levels against several versions of SARS-CoV-2 proteins (S, RBD, N) in home-sampled dried blood spots (DBS). We analyse DBS collected during spring of 2020 from 878 random and undiagnosed individuals from the population in Stockholm, Sweden, and use classification approaches to estimate an accumulated seroprevalence of 12.5% (95% CI: 10.3%-14.7%). This includes 5.4% of the samples being IgG+IgM+ against several SARS-CoV-2 proteins, as well as 2.1% being IgG-IgM+ and 5.0% being IgG+IgM- for the virus' S protein. Subjects classified as IgG+ for several SARS-CoV-2 proteins report influenza-like symptoms more frequently than those being IgG+ for only the S protein (OR = 6.1; p < 0.001). Among all seropositive cases, 30% are asymptomatic. Our strategy enables an accurate individual-level and multiplexed assessment of antibodies in home-sampled blood, assisting our understanding about the undiagnosed seroprevalence and diversity of the immune response against the coronavirus.