Catch-up campaign to vaccinate children against measles
25 April 2013 Last updated at 18:53 BST
Health workers in England are aiming to vaccinate a million young people against measles, following an outbreak in south Wales and a growing number of cases in England.
The catch-up campaign, run through GPs, schools and community groups, will focus on children aged 10 to 16.
Measles is a highly contagious disease characterised by a high fever and a rash, and in one in 15 cases can lead to severe complications and even death.
Fergus Walsh reports.