1 The affiliations of the members of the WHO Ad Hoc Expert Group on the Next Steps for Covid-19 Vaccine Evaluation are the Office of Vaccines Research and Review, Food and Drug Administration, Silver Spring (P.R.K.), the School of Medicine, University of Maryland (M.M.L.), and Johns Hopkins University (S.P.), Baltimore, and the National Institute of Allergy and Infectious Diseases, Bethesda (M.N.) - all in Maryland; the Department of Biostatistics (T.R.F.), Fred Hutchinson Cancer Research Center (T.R.F., E.H.), University of Washington, Seattle; the Department of Biostatistics, University of Florida, Gainesville (I.M.L.); the Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom (R.P., V.B.); the Indian Council of Medical Research, New Delhi (B.B.); the Faculty of Medicine of the Universidad Nacional Autónoma de México, Mexico City (A.C.); the Coalition for Epidemic Preparedness Innovations, London (J.P.C.); the University of Pennsylvania, Philadelphia (S.S.E., S.P.); the University of the West Indies, Kingston, Jamaica (J.P.F.); the World Health Organization, Geneva (A.M.H.-R., M.J.R., S.S.); the Department of Health Security, Finnish Institute for Health and Welfare, Helsinki (H.M.N.);and the Wits Reproductive Health and HIV Institute, University of the Witwatersrand, Johannesburg (H.R.), and the Centre for the AIDS Programme of Research in South Africa, Nelson R. Mandela School of Medicine, University of KwaZulu-Natal, Durban (J.S.) - both in South Africa.