Public Health Wales says vaccinations are being offered to parents in Swansea "on a scale never seen before."
It says the measles virus has continued to circulate and spread among children in the easter holidays, and is expected to spread further among those susceptible now they are back at school.
2013 is expected to be the worst year for measles in the UK for the past two decades. Read more about the illness and how it is treated.
If the Government's top adviser on immunisation thinks the risk of an emergency in England is a possibility, I believe him.