The World Health Organization declared Zika an international emergency after convening a special committee meeting on Monday to deal with the mosquito-borne virus.

According to the WHO's International Health Regulations, a PHEIC is defined as an "extraordinary event" which is determined to:

  • constitute a public health risk to other States through the international spread of disease; and
  • potentially require a coordinated international response.

"This definition implies a situation that: is serious, unusual or unexpected; carries implications for public health beyond the affected State's national border, and may require immediate international action," the WHO said on its website. 

According to WHO procedures, it is the emergency committee that determines whether an outbreak or other public health event constitutes a PHEIC. This committee advises WHO Director-General Dr. Margaret Chan on any measures that should be put in place to respond to the event.

These measures, known as "temporary recommendations," include actions that can be implemented to prevent or reduce the international spread of disease, and avoid unnecessary interference with international traffic.

The committee provides advice to the WHO director-general throughout the duration of the PHEIC, including recommending any necessary changes to the response, and advising on when the PHEIC can be terminated.

At least one member of the committee should be an expert nominated by a state that is being impacted by the public health outbreak, the WHO says.

Health authorities are currently investigating a potential link between the Zika virus in pregnant women in Latin America, and a rare birth defect called microcephaly in their babies. Babies with microcephaly are born with unusually small heads, and can also have incomplete brain development.

Authorities in Brazil first noticed an increase in the number of Zika virus cases last year. Last week, officials said there were  4,180 suspected cases of microcephaly since late October. Of these cases, 270 have been confirmed.

The virus is spread to humans by a species of mosquito known as Aedes aegypti.