Anti-SARS-CoV-2 antibody standard preparation from the WHO now available

Since end of December 2020, the first international reference material, “First WHO International Standard Anti-SARS-CoV-2 Immunoglobulin”, has been available for the standardisation of results of Anti-SARS-CoV-2 antibody test systems. An excellent correlation of the Anti-SARS-CoV-2 QuantiVac ELISA (IgG) with this reference material has already been confirmed. Therefore, the results of the Anti-SARS-CoV-2 QuantiVac ELISA (IgG) can now be issued in standardised units. The standardised determination of antibody concentration plays an important role in the development of COVID-19 vaccines.

The first vaccine against SARS-CoV-2 has been available since the end of last year and another one has recently been approved in the EU.

Both vaccines are based on the so-called S1 antigen of the virus. This mediates the entry of the virus in the human cell via the receptor binding domain (RBD). If the receptor binding domain is blocked by antibodies formed following vaccination, the virus can no longer infect the human cells. However, to achieve effective virus neutralisation, these antibodies must be present in sufficient quantity.

It is still unknown how many antibodies against S1/RBD must be formed after vaccination in order for a person to be protected from COVID-19. It can be assumed that the determination of antibody concentrations will be one of the most important instruments to check for vaccination success. Therefore, the establishment of one or more threshold values (the concentration of antibodies from which immune protection is considered as given) is very likely. The definition of such threshold value is based on the results from large-scale studies or long-term observations and is usually determined by an evidence-based approach.

This requires the antibody concentration to be reliably and comparably determined independently of the test system used. This is only possible if the test systems give out results in standardised units.

The WHO has now officially approved the first international reference material, the “First WHO International Standard Anti-SARS-CoV-2 Immunoglobulin” (NIBSC code: 20/136). This standard presents a clearly defined antibody activity/concentration against which test systems can be matched and which allows standardising the results.

EUROIMMUN had the opportunity to participate in the characterisation of this reference material and was thus able to match the quantitative S1-based antibody test, i.e. the Anti-SARS-CoV-2 QuantiVac ELISA (IgG) to this standard. As a consequence, the test results can now be issued in standardised units. This optimises the use of the ELISA as a valuable support in the quantification and assessment of antibody concentrations achieved through vaccination with respect to a required immunity.