The MMR jab protects against measles, mumps and rubella
The North West of England could be on the verge of a measles epidemic, the Health Protection Agency (HPA) says.
Twenty-two children have been diagnosed with the illness following an outbreak in parts of Cheshire, the third in the region in 2008.
Health officials are urging parents to ensure children get two doses of the MMR vaccine to stop further outbreaks.
Eight confirmed cases in Trafford over the summer were followed by a further 89 in Blackpool, Lancashire.
Dr Rosemary McCann, HPS immunisation lead, said: "We are on the cusp of a measles epidemic and we must do all we can to head it off by encouraging parents to immunise their children."
In the latest outbreak, children aged between one and 12 have been struck down by the illness, with one requiring hospital treatment.
Seven of the cases - in Middlewich, Sandbach, Congleton and Crewe - have been diagnosed by laboratory tests. Further results are awaited.
Dr Sam Ghebrehewet, of the HPA Cheshire and Merseyside unit, said it was important to increase MMR vaccine uptake rates.
"It's worrying that we potentially have 22 cases of measles in Cheshire and my fear is that we will see further outbreaks, here and elsewhere in the region," said the doctor.
Anyone with concerns about measles or the MMR campaign should consult their doctor, the HPA said.