WHO International Standard for anti-SARS-CoV-2 immunoglobulin
Authors: Paul A Kristiansen, Mark Page, Valentina Bernasconi, Giada Mattiuzzo, Peter Dull, Karen Makar, Stanley Plotkin, Ivana Knezevic
Journal: The Lancet (2021)

The development timeline of COVID-19 vaccines is unprecedented, with more than 300 vaccine developers active worldwide.1Le TT Cramer JP Chen R Mayhew S Evolution of the COVID-19 vaccine development landscape.Nat Rev Drug Discov. 2020; 19: 667-668Crossref PubMed Scopus (271) Google Scholar Vaccine candidates developed with various technology platforms targeting different epitopes of SARS-CoV-2 are in the pipeline. Vaccine developers are using a range of immunoassays with different readouts to measure immune responses after vaccination, making comparisons of the immunogenicity of different COVID-19 vaccine candidates challenging. In April, 2020, in a joint effort, the Coalition for Epidemic Preparedness Innovations (CEPI), the National Institute for Biological Standards and Control (NIBSC), and WHO provided vaccine developers and the entire scientific community with a research reagent for an anti-SARS-CoV-2 antibody. The availability of this material was crucial for facilitating the development of diagnostics, vaccines, and therapeutic preparations. This effort was an initial response when NIBSC, in its capacity as a WHO collaborating centre, was working on the preparation of the WHO International Standards. This work included a collaborative study that was launched in July, 2020, to test serum samples and plasma samples sourced from convalescent patients with the aim of selecting the most suitable candidate material for the WHO International Standards for anti-SARS-CoV-2 immunoglobulin. The study involved 44 laboratories from 15 countries and the use of live and pseudotype-based neutralisation assays, ELISA, rapid tests, and other methods. The outcomes of the study were submitted to WHO in November, 2020. The inter-laboratory variation was reduced more than 50 times for neutralisation and 2000 times for ELISA when assay values were reported relative to the International Standard. The International Standard and International Reference Panel for anti-SARS-CoV-2 immunoglobulins were adopted by the WHO Expert Committee on Biological Standardization on Dec 10, 2020.2WHOFirst WHO International Standard for anti-SARS-CoV-2 immunoglobulin.https://www.who.int/groups/expert-committee-on-biological-standardizationDate: 2021Date accessed: March 8, 2021Google Scholar The International Standard allows the accurate calibration of assays to an arbitrary unit, thereby reducing inter-laboratory variation and creating a common language for reporting data. The International Standard is based on pooled human plasma from convalescent patients, which is lyophilised in ampoules, with an assigned unit of 250 international units (IU) per ampoule for neutralising activity. For binding assays, a unit of 1000 binding antibody units (BAU) per mL can be used to assist the comparison of assays detecting the same class of immunoglobulins with the same specificity (eg, anti-receptor-binding domain IgG, anti-N IgM, etc) The International Standard is available in the NIBSC catalogue. Initiatives have been launched for the harmonisation of immune response assessment across COVID-19 vaccine candidates, including the CEPI Global Centralised Laboratory Network.3Coalition for Epidemic Preparedness InnovationsCEPI establishes global network of laboratories to centralise assessment of COVID-19 vaccine candidates.https://cepi.net/news_cepi/cepi-establishes-global-network-of-laboratories-to-centralise-assessment-of-covid-19-vaccine-candidates/Date: Oct 2, 2020Date accessed: March 8, 2021Google Scholar CEPI centralised laboratories will achieve harmonisation of the results from different vaccine clinical trials with the use of common standard operating procedures and the same crucial reagents, including a working standard calibrated to the international standard. The basic tool for any harmonisation is the global use of an International Standard and IU to which assay data need to be calibrated with the use of a reliable method. It is therefore crucial that the International Standard is properly used by all vaccine developers, national reference laboratories, and academic groups worldwide, and that immunogenicity results are reported as an international standard unit (IU/mL for neutralising antibodies and BAU/mL for binding assay formats). In this manner, the results from clinical trials expressed in IU would allow for the comparison of the immune responses after natural infection and induced by various vaccine candidates. This comparison is particularly important for the identification of correlates of protection against COVID-19; should neutralising antibodies be further supported as a component of the protective response, the expression of antibody responses in IU/mL is essential to gather a consensus from several clinical trials and other studies on the titre required for protection. Although the correlate of protection against SARS-2-CoV has not yet been unequivocally defined, antibodies are likely to be at least part of the protective response. The effect of new variants on the evaluation of antibodies is obvious and unequivocal comparisons are required. Reporting the immunological responses from vaccine clinical trials against the International Standard is essential for the evaluation of clinical data submitted to national regulatory authorities as well as to WHO for emergency use listing, especially as placebo-controlled efficacy studies become operationally unfeasible. There will be a substantial effect on the use of the International Standard if regulatory authorities worldwide request data in IU/mL or BAU/mL. We also encourage journal editors and peer reviewers to ensure that the international standard is used as the benchmark in publications and that data from serology assays are reported in International Standard units. We declare no competing interests.