The Department of Health is launching a £20 million campaign to vaccinate a generation of children thought to be the root cause of a measles outbreak.
There were nearly 600 confirmed cases of measles in England during the first three months of this year, that is three times more than during the same period last year.
The worst affected areas in England were the North West, with 179 cases, and the North East, with 175 cases.
Many schools have already sent letters home to parents asking them to immunise their ten to 16-year-olds.
They are thought to be most at risk after a dip in immunisation during the late 1990s/early 2000s, because one doctor wrongly linked the MMR jab to autism.
Experts say all areas are at risk.
In London and the South West the MMR uptake has dropped as low as 70%.
Almost all of the population (95%) needs to be vaccinated to prevent an outbreak.