The Hajj Is a Perfect Laboratory for Disease Warning Systems

Right now, one of the world’s largest mass gatherings is taking place in the desert of Saudi Arabia. The hajj, the yearly pilgrimage to Islam’s holiest sites, is required of every observant Muslim who can perform it. More than 2 million people have poured into the country, over land, by air, and in massive charter deployments, from essentially every place around the globe where Muslims reside.