SARS-CoV-2 Surrogate Virus Neutralization Test (sVNT) Kit (RUO)

The novel coronavirus SARS-CoV-2 that causes the COVID-19 disease, emerged in 2019 and caused a world-wide pandemic. With COVID-19 still spreading and vaccination efforts underway, there is an urgent need for high quality tests to conduct dependable serology and epidemiology studies.

A serological test, also known as an antibody test, searches for antibodies against the SARS-CoV-2 virus in an individual's blood. There are two types of antibody tests for detecting SARS-CoV-2-induced immune response.

The first type of antibody tests investigate a general immunogenic response by detecting either the total antibody response or the isotype-specific response to infection. A number of ELISA and lateral flow rapid tests are on the market allowing users to detect such general binding antibodies.

The second type of antibody tests detect only the portion of the antibodies that can interfere with the binding of the virus to the human cells and deter subsequent infection. These are termed neutralization antibody tests. The gold standard for such tests is the virus neutralization assay (VNT). It requires handling the live SARS-CoV-2 virus and monitoring its interaction with human cells in presence of a sample to determine if the sample contains antibodies that can prevent the virus from binding (neutralizing antibodies). This assay is well-established and has been used for investigating patients' immune response to a variety of infectious diseases. However, VNT is tedious and time-consuming, taking 2-4 days to complete and requiring a high level of expertise. Due to the use of a live virus, the VNT test can only be conducted in a specialized biosafety level 3 (BSL3) containment facility. An alternative to the VNT is a test that uses a non-infectious virus such as lentivirus expressing the viral protein of interest. Such a pseudovirus-based virus neutralization test (pVNT) can be performed in BSL2 level safety environment. However, pVNT is also time-consuming and suffers from many of the shortcomings of the VNT – such as higher experimental variability, the requirement for a high level of expertise, and significant time to obtain results.

To overcome the shortcomings of VNT and pVNT, Professor Lin-Fa Wang's lab at Duke-NUS Medical School established a novel approach - the surrogate virus neutralization test (sVNT). The sVNT detects NAbs without the need to use live virus or cells and can be completed in 1-2 hours in a BSL2 lab. The sVNT assay uses purified receptor binding domain (RBD) from the SARS-CoV-2 viral spike (S) protein and the host cell receptor ACE2. The test is designed to mimic the virus-host interaction by direct protein-protein interaction in a test tube or an ELISA plate well. This highly specific interaction can then be neutralized, i.e., blocked by the NAbs in patient or animal sera in the same manner as in a conventional VNT.

Table 1. The kit has been evaluated in China, Singapore, and USA. Here's the data summary.

Table 2. Data grouped by days.

Table 3. Data using PRNT as comparator