Polio spread in Pakistan described as an 'uncontrolled outbreak'
6 May 2014 Last updated at 04:22 BST
The World Health Organization (WHO) has declared the spread of polio is an international public health emergency.
Outbreaks in Asia, Africa and Middle East are an "extraordinary event" needing a co-ordinated "international response", the agency says.
All residents and long-term visitors of affected countries will need to receive a dose of the vaccine before travelling internationally, and carry with them a certificate proving vaccination.
Kim Ghattas reports from Pakistan, a country suffering "an uncontrolled outbreak" of the virus.