The near eradication of polio is one of the great global public health success stories of the last few decades. Thanks to concerted vaccination campaigns, the number of cases was cut from around 350,000 in 1988 to just 187 in 2012.
Today, however, the World Heath Organization warns that the crippling disease could be making a comeback. At the end of last month, there were 68 confirmed polio cases worldwide, compared to just 24 at the same time last year.
Read more: Polio back as public health emergency
The agency described current polio outbreaks across at least 10 countries in Asia, Africa and the Middle East as an "extraordinary event" that required a coordinated international response. It identified Pakistan, Syria and Cameroon as having allowed the virus to spread beyond their borders, and recommended that those three governments require citizens to obtain a certificate proving they have been vaccinated for polio before traveling abroad.
The disease has also been identified in Nigeria, Ethiopia, Somalia and Kenya. It has spread from Cameroon to Equatorial Guinea and from Syria to Iraq.