Last year saw the highest number of measles cases in England and Wales since records began, the Health Protection Agency has revealed.
The number of confirmed cases jumped by more than a third to 1,348 in 2008 - a trend that the agency has attributed to parents shunning the MMR vaccine.
Health Protection Agency immunisation specialist Mary Ramsay said: "There are still many children out there who were not vaccinated as toddlers over the past decade and remain unprotected.
"Unfortunately this means that measles, which is highly infectious, is spreading easily among these unvaccinated children."
She said eight out of 10 children were now being vaccinated as a result of increasing public confidence in the vaccine but warned that children who had not been vaccinated remained "at real risk".
The agency has been monitoring measles outbreaks since 1995.