The number of measles cases this year has almost doubled following two outbreaks of the illness, health officials have said.
There were 964 cases in England and Wales in the first half of this year, compared with 497 in the same period in 2011, the Health Protection Agency (HPA) said.
A spokesman said the cases had been associated with ongoing outbreaks in Merseyside and Sussex, and a small number of cases had occurred among England's travelling communities.
The number of cases of rubella, or German measles, has also increased. The HPA said 57 cases of the viral infection were reported between January and June – exceeding the annual totals for the previous nine years.
Officials said parents should ensure that their children received the MMR vaccination, which protects against measles, mumps and rubella – before going back to school.
Dr Mary Ramsay, the head of immunisation at the HPA, said: "It's extremely concerning that measles cases are continuing to rise.
"It's vital that children receive both doses of the MMR vaccination and ahead of returning to school after the holidays, we are urging parents to ensure their children have received the two doses."