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Why do large pilgrimages to Mecca create challenges for preventing the international spread of polio?

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Polio vaccine — polio A health care worker giving a polio vaccine to a child in Katsina state, Nigeria, 2014.

Large pilgrimages to Mecca, specifically the hajj and ‘umrah, present significant challenges for polio eradication because they involve large-scale movements of people from regions where the poliovirus remains endemic.1

These mass gatherings facilitate the potential international spread of the disease, as travelers from polio-endemic countries can inadvertently export the virus to polio-free nations. Because the virus is highly infectious and can be transmitted by individuals who may not show symptoms, the convergence of millions of pilgrims from diverse geographic areas creates a high-risk environment for transmission. Managing these population movements is a critical component of global efforts to prevent the reintroduction of polio into areas where it has already been eliminated.1