The number of cases of measles has reached its highest level for 18 years, health experts said.
There were 2,016 confirmed cases in England and Wales in 2012 - the highest annual total since 1994, the Health Protection Agency (HPA) confirmed.
A spokeswoman said the majority of cases occurred in Merseyside, Surrey and Sussex, as well as several smaller outbreaks in travelling communities.
Measles is a highly-infectious disease and last year health officials noted "prolonged" outbreaks in Merseyside, Surrey and Sussex, an HPA spokeswoman said.
Symptoms include fever, cold-like symptoms, red eyes, sensitivity to light and greyish white spots in the mouth and throat. After a few days a red-brown spotty rash will appear. In severe cases it is potentially fatal.
People are protected against measles, mumps and rubella with the combine MMR vaccine - which is normally given as part of children's routine vaccinations.
Dr Mary Ramsay, head of immunisation at the HPA, said: "Coverage of MMR is now at historically high levels but measles is highly infectious and can spread easily among communities that are poorly vaccinated, and can affect anyone who is susceptible, including toddlers in whom vaccination has been delayed.
"Older children who were not vaccinated at the routine age, who may now be teenagers, are at particular risk of becoming exposed, while at school for example."
She added: "Measles is often associated with being a disease of the past and, as a result, people may be unaware that it is a dangerous infection that can lead to death in severe cases.
"Parents should ensure their children are fully protected against measles, mumps and rubella with two doses of the MMR vaccine."