Updated on 6 May 2014
The vast majority of new cases are in Pakistan, where the WHO has set up an independent monitoring board.
At the end of last month, there were 68 confirmed polio cases worldwide, compared with just 24 at the same time last year. In 2013, polio reappeared in Syria, sparking fears the civil war there could ignite a wider outbreak as refugees flee to other countries across the region. The virus has also been identified in the sewage system in Israel, the West Bank and Gaza, although no cases have been spotted.
In February, the WHO found that polio had also returned to Iraq, where it spread from neighboring Syria. It is also circulating in Afghanistan (where it spread from Pakistan) and Equatorial Guinea (from neighboring Cameroon) as well as Nigeria, Ethiopia, Somalia and Kenya. Officials also worry countries torn by conflict, such as Ukraine, Sudan and the Central African Republic, are rife for polio reinfection.