WHO international standard for SARS-CoV-2 antibodies to determine markers of protection.

Competing Interests: CWT, WNC, and L-FW are co-inventors of the surrogate virus neutralisation technology that has been commercialised under the trade name cPass by GenScript Biotech. GM provided independent expertise on the calibration of assays using the WHO IS. There is no endorsement of any individual assay, diagnostic product or vaccine by the NIBSC authors (GM and NJR). We thank Yun Sun, Wan Su, Lam Anh Nguyet, Tran Tan Thanh, Shuting Xu, and Yanfeng Li for technical assistance and coordination of different study groups.