Abstract
High-throughput detection of neutralizing antibodies against SARS-CoV-2 presents a valuable tool for vaccine trials or investigations of population immunity. We evaluate the performance of the first commercial surrogate virus neutralization test (sVNT, GenScript Biotech) against SARS-CoV-2 plaque reduction neutralization test (PRNT) in convalescent and vaccinated individuals. We compare it to five other ELISAs, two of which are designed to detect neutralizing antibodies. In 491 pre-vaccination serum samples, sVNT missed 23.6% of PRNT-positive samples when using the manufacturer-recommended cutoff of 30% binding inhibition. Introducing an equivocal area between 15 and 35% maximized sensitivity and specificity against PRNT to 72.8–93.1% and 73.5–97.6%, respectively. The overall diagnostic performance of the other ELISAs for neutralizing antibodies was below that of sVNT. Vaccinated individuals exhibited higher antibody titers by PRNT (median 119.8, IQR 56.7–160) and binding inhibition by sVNT (median 95.7, IQR 88.1–96.8) than convalescent patients (median 49.1, IQR 20–62; median 52.9, IQR 31.2–76.2). GenScript sVNT is suitable to screen for SARS-CoV-2-neutralizing antibodies; however, to obtain accurate results, confirmatory testing by PRNT in a equivocal area is required. This equivocal area may require adaptation for use in vaccinated individuals, due to higher antibody titers.
Highlights
Over the course of the COVID-19 pandemic and especially with the availability of several vaccines, the detection of neutralizing antibodies as a potential marker of immunity has become increasingly important for use in vaccine trials, to establish individual vaccination success or to evaluate the population immunity to infection and disease
The GenScript surrogate virus neutralization tests (sVNT) is based on a two-step process: firstly, the recombinant HRP-coupled receptor-binding domain (RBD) is pre-incubated with serum, leading to binding of RBD by present RBD-specific antibodies; and secondly, addition of the mixture to the enzyme-linked immunosorbent assays (ELISA) plate where antibody-bound RBD and any unbound RBD will compete for binding to the coated angiotensin-converting enzyme 2 (ACE2) receptor
Neutralizing antibodies are considered to block the binding between RBD and ACE2, increasing the amount of free RBD that can bind to the plate
Summary
Over the course of the COVID-19 pandemic and especially with the availability of several vaccines, the detection of neutralizing antibodies as a potential marker of immunity has become increasingly important for use in vaccine trials, to establish individual vaccination success or to evaluate the population immunity to infection and disease. While it is still under discussion whether there is a certain antibody titer that confers protection to SARS-CoV-2 (correlate of protection), as is the case for other viruses—for example, for Hepatitis B virus an antibody titer above 10 mIU/mL is associated with protection against infection1—, recent studies suggest that neutralizing antibodies present a good estimate for protection against SARS-CoV-22,3
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