A "national incident" has been declared as measles cases soar in parts of England and Wales.
Some children who have not been vaccinated are being forced to isolate for weeks in the West Midlands.
More than 300 cases have been classed as confirmed or likely in the area since October 2023.
This follows a drop in uptake of the preventative MMR vaccination against the illness.
Unvaccinated children may be forced to isolate
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Children who had missed both doses of MMR and are in areas with known cases have been sent home from school in Birmingham.
Some unvaccinated children have been asked to stay off school and instructions are being given on a case-by-case basis.
Birmingham City Council wrote to parents saying children could have to isolate for "three weeks" which could "disrupt their learning" if it happens repeatedly.
The UK Health Security Agency said: “There have been children who have had to stay off school because of being a contact with a person with measles and being unvaccinated.
"If they have had one dose they can stay in school, but if they have had neither they are asked to stay off.”
Jab clinics are being held in schools in the West Midlands for parents, staff and children who have missed to vaccination.
Cases in the West Midlands are the highest since the mid 1990s.
There were 57 suspected cases in the area in December making up a huge part of the 217 cases for the whole of England.
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Measles cases are at their worst since the 1990s in some parts of the UK
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Anyone who is unvaccinated can get measles but it is most common in young children.
It causes cold-like symptoms, a high fever, aches and pains and swollen and watery eyes.
It is highly contagious and can lead to "potentially life-threatening complications" in some cases, according to the NHS.
A measles outbreak was first reported in the UK last year.
Speaking at the time, consultant in health protection for Public Health Wales Sion Lingard said: “Links have been found between all seven cases so while there is currently no evidence of wider community transmission, measles is an extremely contagious infection and we are concerned that people who are not protected by vaccination could be at risk."