Dr Tony Hill, Joint Director of Public Health in Lincolnshire, is urging teenagers to go and get vaccinated against measles.
Letters are being sent out to the parents of up to ten thousands 10 to 16 year olds in Lincolnshire, who it's feared aren't fully protected against measles.
The Joint Director of Public Health for the county says thousands of youngsters didn't receive two doses of the MMR jab when they were younger due to a low uptake, so aren't fully protected.
Even those that have had measles are being advised to still have both doses of the vaccine. The action follows a large outbreak of the infectious disease in parts of Wales.