Latest figures show that one in 12 of the ten to 16-year-olds in Bath and north east Somerset have not been vaccinated against measles.
Cases of the disease are on the rise, following an outbreak in Wales that has seen 80 people hospitalised.
There have been no recent cases in B&NES.
But health officials are urging parents to take simple steps to ensure their children are protected.
Measles, which for many years was extremely rare, is showing signs of coming back for the simple reason that not enough children have been fully vaccinated and so are susceptible to infection.
The latest figures were presented to local health chiefs at a meeting this week.
Parents can prevent their child from catching the virus with two doses of the MMR vaccine.
A national catch-up programme to increase vaccination uptake in children and teenagers in England will now be introduced through GPs and schools.
The current problems have been blamed on the alarm spread by widespread publicity over discredited research by former King Edward's School pupil Dr Andrew Wakefield suggesting a link between the MMR vaccine and autism.