A measles 'epidemic' is underway and cases appear to be increasing, warned global health leaders about the highly contagious disease.
Parents have been urged to vaccinate their children by the World Health Organization (WHO).
It raised concerns that a dip in vaccination uptake during the Covid-19 pandemic could be behind a rise in cases compared to what would usually be expected in the first two months of the year.
Problems with accessing care and questions over vaccination which arose during the pandemic could have led to fewer people getting the jab, it suggested.
"We've got really good vaccination programmes all over Europe to keep kids safe and one of them is the vaccination programme against measles, but it's been slowed down because Covid has really taken up so much of healthcare," said Dr David Nabarro, the WHO's special envoy for Covid-19, to Sky News.
"And so we've got an awful lot of people who have missed out on measles vaccination – 73 million throughout the world.
"And that's meant that this year, in the first few months, there have been 17,000 cases of measles globally, whereas in the first two months of the previous years, it's usually been lower – 10,000 or less.
"So yes, we've got a global measles epidemic, and that worries us because measles can be a very dangerous disease.
"We've just got to get the vaccinations working again and that's part of getting health services working again as Covid settles into a more regular position in our lives."
He added: "A lot of folk have actually thought to themselves: 'well, with all this fuss and bother about Covid, perhaps we won't take our kids to be immunised, and any way it's quite difficult because doctor surgeries have been using different working arrangements'.
"My main request to everybody – please get your child vaccinated, please talk to the local nurse or doctor about vaccination options.
"It really matters. It's so important. And with measles, the more people who get vaccinated, the more likely we are to get the whole measles outbreaks under control."
Last week, the WHO and Unicef warned there is a "perfect storm of conditions for measles outbreaks".
The organisations said that an increase in cases around the world in January and February were "worrying" and could trigger larger outbreaks.
Some 17,338 measles cases were reported worldwide in January and February 2022, compared to 9,665 during the first two months of 2021.
The organisations said that about 73 million children are at risk of measles due to missed vaccinations.
It echoes similar warnings issued by UK health officials in February.
The UK Health Security Agency said that uptake of the measles, mumps and rubella (MMR) vaccine has dropped to the lowest level in a decade.
Coverage of the first dose of the MMR vaccine in two year olds dropped below 90 percent, it said.
And 85.5 percent of five-year-olds in England have had both doses of the jab, the health body said in February.
Meanwhile, an opinion piece published in The BMJ last week warned that even a small reduction in MMR uptake can have a "canary in a coalmine" effect and lead to disease outbreaks.
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