A public health emergency of international concern is a formal declaration by the World Health Organization (WHO) of "an extraordinary event which is determined to constitute a public health risk to other States through the international spread of disease and to potentially require a coordinated international response", formulated when a situation arises that is "serious, sudden, unusual, or unexpected", which "carries implications for public health beyond the affected state's national border" and "may require immediate international action". Under the 2005 International Health Regulations (IHR), states have a legal duty to respond promptly to a PHEIC. The declaration is publicized by an IHR Emergency Committee (EC) of international experts, which was developed following the 2002–2004 SARS outbreak.

The 2013–2016 epidemic of Ebola virus disease, centered in Western Africa, was the most widespread outbreak of the disease in history. It caused major loss of life and socioeconomic disruption in the region, mainly in Guinea, Liberia and Sierra Leone. The first cases were recorded in Guinea in December 2013; later, the disease spread to neighbouring Liberia and Sierra Leone, with minor outbreaks occurring in Nigeria and Mali. Secondary infections of medical workers occurred in the United States and Spain. In addition, isolated cases were recorded in Senegal, the United Kingdom and Italy. The number of cases peaked in October 2014 and then began to decline gradually, following the commitment of substantial international resources.