Outbreaks in Asia, Africa and Middle East are an "extraordinary event" needing a co-ordinated "international response", the agency says.

 

It recommends citizens of affected¹ countries travelling abroad carry a vaccination² certificate.

 

It says Pakistan, Cameroon, and Syria "pose the greatest risk of further wild poliovirus exportations in 2014."

 

The WHO recorded 417 cases of polio worldwide for the whole of 2013. For 2014, it had already recorded 68 cases by 30 April - up from 24 in the same period last year. 

 

Polio mainly affects children under five years old. 

 

The virus is transmitted through contaminated food and water, and multiplies in the intestine³. It can then invade the nervous system, causing paralysis⁴ in one in every 200 infections. It is capable of causing death within hours.

 

 

"The conditions for a public health emergency of international concern have been met," said Bruce Aylward, WHO Assistant Director General.

 

He was speaking after last week's emergency meeting in Geneva on the spread of polio which included representatives of the affected countries. 

 

"The international spread of polio to date in 2014 constitutes an 'extraordinary event' and a public health risk to other states for which a co-ordinated international response is essential," the WHO's International Health Regulations Emergency Committee said in statement.

 

"If unchecked, this situation could result in failure to eradicate⁶ globally one of the world's most serious vaccine⁷ preventable diseases." 

 

The WHO also lists Afghanistan, Equatorial Guinea, Ethiopia, Iraq, Israel, Somalia and Nigeria as "posing an ongoing risk for new wild poliovirus exportations in 2014."

 

It is only the second time in the WHO's history it has made such a declaration, the first being during the swine flu pandemic of 2009, the BBC's Imogen Foulkes in Geneva reports.

 

The polio virus is endemic in just three countries - Pakistan, Afghanistan, and Nigeria. But attacks on vaccination campaigns in Pakistan in particular have allowed the virus to spread across borders.

 

Syria, which was polio-free for 14 years, was re-infected with the virus from Pakistan. 

 

Refugees are still pouring out of Syria, to Jordan, Lebanon and Turkey, and checking whether all of them have been vaccinated⁸ will be impossible, our correspondent says.

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