A number of confirmed cases of measles across Sussex and Surrey has led to the Health Protection Agency (HPA) issuing an alert to families travelling abroad.
It said a small number of schools in the counties had reported cases in the past few weeks.
The HPA urged families going abroad for the Easter holidays to ensure they were up to date with their MMR vaccines.
It said the advice followed a large outbreak of measles in France and cases in Italy, Germany and Bulgaria.
Measles can be caught at any age, but it is most common among children, teenagers and young adults who have not been immunised.
The HPA said complications affected one in every 15 children and could include eye and ear infections, pneumonia, seizures and rarely encephalitis.