Formal declaration by the World Health Organization (WHO) of "an extraordinary event which is determined to constitute a Global 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 global 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 Emergency Committee (EC) made up of international experts operating under the IHR (2005), which was developed following the SARS outbreak of 2002–03.
Since 2009 there have been six PHEIC declarations: the 2009 H1N1 (or swine flu) pandemic, the 2014 polio declaration, the 2014 outbreak of Ebola in Western Africa, the 2015–16 Zika virus epidemic, the ongoing 2018–20 Kivu Ebola epidemic, and the ongoing 2019–20 coronavirus pandemic. The recommendations are temporary and require reviews every three months.
SARS, smallpox, wild type poliomyelitis, and any new subtype of human influenza are automatically PHEICs and thus do not require an IHR decision to declare them as such. A PHEIC is not confined to infectious diseases, and may cover an emergency caused by exposure to a chemical agent or radioactive material. In any case within its ambit, it is a "call to action" and "last resort" measure.