London is at risk of a measles outbreak, because at the height of the MMR scare - it had the lowest rate of MMR vaccination in the country.
The capital is singled out for a warning by health bosses, as they launch a so-called "catch up" programme - aimed at teenagers who haven't been inoculated.
Liz Wickham reports.
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.