The number of cases of measles has reached its highest level for 18 years, health experts say.
There were 2,016 confirmed cases of the highly infectious disease in England and Wales in 2012 – the highest annual total since 1994, according to the Health Protection Agency (HPA).
A spokeswoman said the majority of cases occurred in Merseyside, Surrey and Sussex, where "prolonged" outbreaks were noted last year. Several smaller outbreaks occurred in travelling communities.
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 combined 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.
"Measles continues to circulate in several European countries that are popular with holidaymakers. Measles is a highly infectious disease, so the only way to prevent outbreaks is to make sure the UK has good uptake of the MMR vaccine, and that when cases are reported, immediate public health action is taken to target unvaccinated individuals in the vicinity as soon as possible."