Estimating Social Contacts in Mass Gatherings Through Agent-Based Simulation Modeling: Case of Hajj Pilgrimage

Most mass gathering events have been suspended due to the SARS-CoV-2 pandemic. However, with vaccination rollout, whether and how to organize some of these mass gathering events arises as part of the pandemic recovery discussions, and this calls for decision support tools. Hajj, one of the world's largest religious gatherings, was substantively scaled down in 2020 and it is still unclear if it will take place in 2021 and sub-sequent years. Considering the disease trends and vaccination conditions in the pilgrims’ country of origin, and the operational and logistical aspects of implementing public health measures, Hajj reopening conditions could be very complex. Simulating disease transmission dynamics during the Hajj season under differ-ent conditions can provide some insights for better decision-making. Since most disease risk assessment models require data on the number and nature of possible close contacts between individuals, we seek to use integrated agent-based modeling and discrete events simulation techniques to capture risky contacts among the pilgrims in one of the Hajj major sites, namely Masjid-Al-Haram. In particular, we assessed different scenarios concerning the total number of pilgrims and enforced physical distancing measures. Our simulation results show that a plethora of risky contacts may occur during the rituals. Also, as the total number of pilgrims increases at each site, the number of risky contacts increases, and physical distancing measures may be challenging to maintain beyond a certain number of pilgrims in the site.