More than half a million children in the UK have not been vaccinated against measles, new figures covering an eight-year period show.
The charity Unicef warned that increasing numbers of youngsters are being left unprotected against measles, which can cause disability and death.
The warning comes after reports that outbreaks of measles were worse in Yorkshire than any other part of the North of England between 2017 and 2018.
With at least 25 total cases of the deadly disease reported last year, the numbers are worse than Lancashire and the North East who reported no more than seven cases.
Read more: How to avoid measles and what to do if you catch it
Unicef is now warning that inaccurate and misleading anti-vaccination messages on social media are thought to be one reason why inoculation rates are plummeting.
The charity's analysis shows that an estimated 169 million children around the world missed out on the first dose of the measles vaccine between 2010 and 2017 - an average of 21.1 million a year.
A list of 10 high-income countries shows the US has the highest number of children missing out on their first dose of the vaccine.
Between 2010 and 2017, some 2,593,000 youngsters in the US did not have their first dose of the vaccine.
The second most affected country was France, with 608,000 unvaccinated children over the same time period, followed by the UK, with 527,000.
Other countries including Argentina, Italy, Japan, Canada, Germany and Australia also made the top 10.
Unicef executive director Henrietta Fore said: "The measles virus will always find unvaccinated children.
"If we are serious about averting the spread of this dangerous but preventable disease, we need to vaccinate every child, in rich and poor countries alike."
In the first three months of 2019, more than 110,000 measles cases were reported worldwide - up almost 300 per cent on the same period the year before.
An estimated 110,000 people, most of them children, died from measles in 2017, a 22% rise on the previous year.
Children need two doses of the vaccine for protection, with the World Health Organisation (WHO) recommending 95 per cent coverage to achieve herd immunity, which offers protection against the disease spreading in the community.
In the UK in 2017, there were 259 measles cases in England, rising to 966 in 2018.
In 2016 and 2017, uptake of the first dose of the MMR vaccine in five-year-olds in the UK exceeded 95 per cent for the first time.
However, two doses of MMR vaccine are required to ensure full protection from measles.
Uptake of the second dose of MMR in five-year-old children is 88 per cent - well below the 95 per cent WHO target.
Globally, 85 per cent of children received their first dose in 2017 and 67 per cent got the second dose.
Unicef said the rates reflected "lack of access, poor health systems, complacency, and in some cases fear or scepticism about vaccines".
Ms Fore said: "Measles is far too contagious.
"It is critical not only to increase coverage but also to sustain vaccination rates at the right doses to create an umbrella of immunity for everyone."