Around a million children and teenagers are to be targeted in a national catch-up vaccination campaign aimed at curbing a rise in measles cases in England.
GP surgeries, schools and community programmes will be used to vaccinate children and young people who have not had either one or two doses of the measles, mumps and rubella (MMR) vaccine in a £20 million campaign.
The scheme has been launched after new figures from Public Health England (PHE) revealed that there were 587 confirmed measles cases in the first three months of this year in England, more than three times the 168 cases in the same period of 2012.
The highest regional total was in the North West at 179, followed by 175 in the North East.
Out of the total number of confirmed cases this year, nearly one in five - 20%, or 108 cases - were admitted to hospital, with 15 of these experiencing complications such as pneumonia, meningitis and gastroenteritis.
The figures, if unchecked, put England on course for another record annual high in measles cases after 1,920 confirmed cases last year.
The rise comes in spite of the highest ever national MMR vaccination level being achieved in England with 94% of five-year-olds receiving one dose and 90% receiving two doses according to the latest PHE figures.
The leap in the number of confirmed cases can mostly be attributed to the proportion of unprotected 10 to 16-year-olds who missed out on vaccination in the late 1990s and early years of 2000 when fears about the discredited link between autism and the vaccine was widespread, according to public health experts.
Children are offered an MMR vaccine at 12 to 13 months, giving 95% protection and then a second dose at around three-and-a-half-years-old which boosts this protection to 99%.
An estimated one third of a million 10 to 16-year-olds who are unvaccinated will be made a "first priority" in the new campaign.
This will be followed by a further estimated third of a million children in this age group who need at least one further MMR jab to give them full protection and another estimated one third of a million children above and below this age group who need at least one further MMR vaccination.
Dr Mary Ramsay, PHE head of immunisation, said there was particular concern about the potential for measles outbreaks in London, the South and East of England where MMR vaccination rates have not been historically as high as other areas in the north of the country.
"We have this legacy of older children who were not vaccinated as toddlers and these young people are now secondary school age," she said.
"So they are now at the position where they can spread infection very effectively."
She added: "Our concern is that we have a potential for school outbreaks in many areas of the country - probably the areas most likely to be affected would be London and the South and East of the country where we know that the historical coverage was not as high as it was in the northern parts of the country."
The figures for England follow a measles outbreak in the south west Wales region where the total number of people who have contracted the disease now stands at 886.
Professor David Salisbury, director of immunisation at the Department of Health, said: "The situation in Swansea, I believe, is a wake-up call for parents - for parents who for whatever reason, quite a few years ago chose not to vaccinate their children and for whom these days vaccines aren't really things that they think about very much.
"But what happened and is continuing to happen in Swansea can happen anywhere in England.
"Whilst this may sound slightly odd, you can of course catch measles but you can't catch up with measles - what I mean is that chasing measles is a forlorn exercise.
"You have to prevent measles and that means we need to get ahead before we have got large numbers of cases and large outbreaks occurring in England."
He added that measles spreads like "wildfire".
"If you think your child has not had one or even two doses of MMR, for goodness sake contact your GP and get it sorted out," he said in a direct message to parents.
"I think that the message from Swansea is very clear and it is trivialised at the risk of your children's health."
He said he was concerned about the situation in London with its densely packed population where there was traditionally a high turnover of residents.
"London to their credit has done a great deal of good work recently and they really have pulled up their immunisation coverage, but that is age-appropriate, that is for their young children," he said.
"They did do a catch-up programme but I would be surprised if they got all of the (unprotected youngsters).
"People are densely packed together in London and that is just what measles likes for high levels of transmission, so I worry about London."
Talking about the risks of measles, he said: "The risk of measles in terms of complications and death is particularly in the under ones, who we really can best protect by preventing them being exposed and the risk goes up again as you get older.
"The risk now for measles in teenagers and adolescents ... of actually measles being a much more serious illness is staring at us."
The appeal comes after shamed doctor Andrew Wakefield was struck off the medical register for his discredited research which claimed to find a link between autism and the MMR vaccine.
The study, published in 1998, caused a global scare and uptake levels of the vaccination - which protects against MMR - fell significantly in the years after its publication.
Measles, described as one of the most infectious diseases known to man, can lead to serious complications, including blindness and even death.
The virus is contained in the millions of tiny droplets that come out of the nose and mouth when an infected person coughs or sneezes.Suggest a correction