RG receives consulting fees from WHO. All other authors declare no competing interests. We thank the event organisers and health authorities for engaging with WHO on mass-gathering decision making and implementation. We thank members of the WHO Incident Management Teams for COVID-19 in WHO headquarters and regional offices. We are particularly grateful to the mass-gatherings teams in WHO regional offices for their contributions to the identification and monitoring of mass-gathering events. We also thank the members of the COVID-19 Epidemiology Pillar at WHO headquarters (Geneva, Switzeralnd) for their contributions to the figure and Maria Van Kerkhove (WHO, Geneva, Switzerland). We are grateful to Vanessa Grégoire, Clint Haines, Noelle Huhn, Crystal Watson, Murhaf Alkaddour, Camille Clausse-Pujo, Lauren Formica, Stephanie Marie Kenyon, Oyinkansola Oladapo, and Zeba Nauroz (Johns Hopkins Center for Health Security, Johns Hopkins University, Baltimore, MD, USA) for their contributions to database development and management.