Three students from Park Community School in Barnstaple are off school with suspected cases of measles.
The Health protection Agency is working with NHS Devon and the school to make sure pupils and parents are well informed.
An email sent to all parents today gives advice on how best to avoid contracting the disease.
Measles is highly infectious and can cause serious complications in vulnerable people.
The email asks parents and guardians to ensure all children and babies over the age of one-year-old have received two doses of the MMR vaccination.
The three suspected cases have occurred in children who have either not been immunised or only partially immunised with the Measles, Mumps and Rubella (MMR) vaccine.
Symptoms of measles include the following:
•cold-like symptoms, such as a runny nose
•watery and painful eyes (conjunctivitis)
•a mild to severe temperature
•aches and pains
•red-brown spotty rash that usually starts behind the ears and spreads to the head and neck on to the rest of the body