The Government is launching a £20 million campaign to vaccinate a generation of children thought to be the cause of a measles outbreak.
This year is on course to be the worst year for measles outbreaks in two decades.
Already, in the first three months there have been 587 cases in England.
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The capital has the lowest level of MMR vaccination take up in the country, and this puts it at particular risk of suffering a measles outbreak.
With the number of cases of the disease already rising, Public Health England are so concerned they're launching a catch-up vaccination programme.
They're particularly concerned about those aged 10-16 who may have missed out on the vaccine in the wake of the Andrew Wakefield scandal.
There have so far been 68 cases of measles in the capital so far this year- compared to just 137 for the whole of last year.
London could be next part of the country to be affected by the measles outbreak that is gripping South Wales. The warning comes from Dr David Elliman, an immunisation expert from the Royal College of Paediatrics and Child Health.
The capital is at risk because it has the lowest uptake of MMR Vaccinations in the UK.