Public Health England (PHE) has said it is currently aware of 10 cases of measles across the East Midlands, including a confirmed case in Loughborough yesterday.
The statistics come as it was revealed 7,000 young children in the region are not fully up-to-date with routine immunisations.
In the UK, the first dose of the MMR vaccine,
which protects against Measles, Mumps and Rubella, is given to infants at 12 months and a second dose before school at three years old, which is needed for children to be considered fully protected.
PHE said 2,000 five-year-olds in the region still needed their first dose of the MMR vaccine, leaving them "significantly more at risk" than other pupils.
Meanwhile, thousands more still need their second dose or pre-school booster.
Dr Vanessa MacGregor, from PHE East Midlands, said: "It's a real concern so many
young children in our region could be starting school without the full protection
that the NHS offers for free."
She said they had particular concerns about children not being protected against measles which had seen outbreaks in the East Midlands in the past year.
New 999 centre could lead to better response times
Response times to 999 calls could be improved thanks to all three emergency services working under one roof in Lincolnshire, fire chiefs say.
Fire and ambulance crews have begun moving into a £21m building on South Park in Lincoln, and police officers are due to move into the centre later this year.
It's the first combined fire, ambulance and police station in the country.
We've seen it already at Sleaford and Louth where the operational crews from fire and EMAS have been working together for sometime. You can see on the ground the improvement in operational procedures when we attend things like road traffic accidents, for example.
Watch: Today's weather for the East Midlands
BBC weather presenter
Well, at least it's stopped raining...
It's set to be a mostly cloudy day with some bright spells, but there's better news on the way for the weekend.