A risk-based approach is best for decision making on holding mass gathering events.

Memish and colleagues, in their response to our Comment, perceive conflict between the current best-practice risk management advice on physical distancing and the scientific evaluation of cancelling or continuing mass gathering events during the coronavirus disease 2019 (COVID-19) pandemic. Although we have already acknowledged the need to balance these two considerations in order to maintain public understanding and trust, we do not accept that conflict is inevitable as our approach requires all mass gatherings to be considered in context, including the prevailing advice on physical distancing and movement restrictions. An open and transparent process to explicitly consider the risks of a mass gathering can, in fact, promote public confidence in the decision.

The validity of our approach is exemplified by the emergence of the novel Middle East respiratory syndrome coronavirus (MERS-CoV) in Saudi Arabia in 2012. MERS has a fatality rate 10–15 times greater than COVID-19, and has spread globally; it has significant epidemic potential (as illustrated by the MERS-CoV outbreak in South Korea) and remains on the WHO Blueprint List of priority pathogens, yet we have never advocated cancelling the annual Hajj pilgrimage in the epicentre of MERS activity. This was because we adopted a risk-based approach and concluded that the risks were manageable in the context of the mitigation measures that Saudi Arabia had put in place; 7 years of safe and successful Hajj since MERS-CoV emerged suggests that the decision was correct. We have not yet seen what decisions might be made by the Saudi Government about the impending Hajj in 2020, in the context of COVID-19, but we urge that those decisions are made on the basis of an evidence-based risk assessment process such as the one we describe in our Comment.

Any risk assessment and risk management framework for a mass gathering might inherently result in cancellation or postponement, as in the recent decision by the International Olympic Committee and Japanese Government to postpone the 2020 Olympic Games. In the current COVID-19 pandemic, it is inevitable in many countries that the outcome will be to cancel or postpone events, either because the risk is too great or because the capacity for mitigation measures is not available, or both. That is an appropriate and valid use of a risk assessment tool. The evidence base for mass gathering health is still evolving and needs to be expanded, and risk assessment frameworks also need to be refined further. Preventing global spread of infectious diseases from mass gathering events and protecting global health security require public health decisions based on evidence and an agreed rational framework for decision making. A systematic process to assess the event encourages us to consider explicitly the reasoning behind the decision, what we expect the decision to achieve, and what evidence exists to support that reasoning. This, in turn, helps us evaluate whether the decision achieves what is expected and so informs future decisions. It also requires consideration of the negative impacts of a decision to cancel an event (jobs, mental health, the economy) and to look for ways to mitigate the adverse effects.

Crucially, we must look to the future. Whatever the course of the COVID-19 pandemic, countries, individually and collectively, will reach a point when they want to start removing restrictions and rebuild communities and economies. This will include decisions on re-starting mass gatherings. These decisions will need to be carefully reviewed and phased to ensure that the COVID-19 pandemic is not reignited; here, we advocate our risk-based approach as a sensible and rational way forward to consider those decisions.