When the Expanded Programme on Immunization (EPI) was established 40 years ago, only around 5% of the world's children were protected from six diseases — polio, diphtheria, tuberculosis, pertussis, measles and tetanus — targeted by four vaccines. Today, that figure is 83%, with some developing countries reaching 99% immunization coverage. What started as an ambitious effort to tackle six vaccine-preventable diseases has become one of the world's most successful public health programmes.

More information: http://www.who.int/immunization/programmes_systems/en/