'Don't be taken in by anti-vaccine myths on social media'
People who believe the myths spread by anti-vaccine campaigners "are absolutely wrong", England's top doctor has said.
Prof Dame Sally Davies said the MMR vaccine was safe and had been given to millions of children worldwide but uptake was currently "not good enough".
In England, 87% of children receive two doses but the target is 95%.
The chief medical officer urged parents to get their children vaccinated and ignore "social media fake news".
Her comments come on the 30th anniversary of the measles, mumps and rubella (MMR) vaccine being introduced in the UK.
She said myths peddled about the dangers of vaccines on social media was one reason parents weren't taking their children to get the MMR vaccine.
"A number of people, stars, believe these myths - they are wrong," she said.
"Over these 30 years, we have vaccinated millions of children.
"It is a safe vaccination - we know that - and we've saved millions of lives across the world.
"People who spread these myths, when children die they will not be there to pick up the pieces or the blame."
The MMR vaccine has dramatically reduced cases of measles, mumps and rubella and saved about 4,000 deaths from measles, resulting in the UK being declared "measles free" by the World Health Organization last year.
This means the disease is no longer native to the UK, although cases do still occur.
However, Dame Sally said there had been too many cases of measles in England this year - 903 so far, and young people who had missed out on the MMR vaccine had been particularly affected.
Uptake of the MMR vaccine had reached a good level in previous years but has now dropped back to 87%.
"That means a lot of protection but it doesn't give us herd immunity," Dame Sally said.
"So when people from abroad have been coming in, travelling infected, it is spreading into our local communities."
The MMR vaccine is given on the NHS as a single injection to babies, usually within a month of their first birthday.
They then have a second injection before starting school, when three years old.
Children who missed an earlier MMR vaccination can have a "catch-up" jab on the NHS.
Single measles, mumps and rubella vaccines are available but not on the NHS in the UK.
In 1998, a study by former doctor Andrew Wakefield incorrectly linked the MMR vaccine to autism. The research is now completely discredited.
But it had an impact on the coverage of the vaccine, which dropped to about 80% in the late 1990s and a low of 79% in 2003.
Numerous public health campaigns have increased uptake in the years since.