In 2014, together with colleagues from Public Health England, World Health Organization, London School of Hygiene and Tropical Medicine, and the Middle East, Zumla co-led The Lancet series on Mass Gatherings Medicine which was launched at the World Health Assembly of Ministers of Health in Geneva. This was a Series of reports about different mass gatherings: the London 2012 Olympic and Paralympic Games; the 2012 European Football Championship finals, hosted jointly by Poland and Ukraine; and the 2012 and 2013 Hajj. These reports set out the planning and surveillance systems used to monitor public health risks, and describe the public health experiences and lessons learnt for the planning of future events.