Three of the four suspected cases of measles reported in children in Tyne and Wear were confirmed last night.
It was also revealed that the three positive cases in Gateshead and South Tyneside had not had MMR jabs.
Doctors at Gateshead and South Tyneside Health Authority say the history of the fourth possible victim suggests it will not have contracted the disease.
The confirmed cases were first reported last Monday and come after five cases were confirmed in County Durham in November and December last year.
There are also three suspected cases on Teesside and four in Northumberland.
Dr Bashir Malik, consultant in communicable diseases at the health authority, said he feared more cases if some mothers refused to give their children the triple MMR jab against measles, mumps and rubella.
He said: "Unfortunately the confirmed cases had not had the MMR injection. If they had it would have protected them from measles.
"The results for the fourth case are awaited but from the history taken from the GP it does not like it is a measles case.
"I am concerned that it is the first time in five years we have had positive cases here. Our uptake for MMR here is 91.4 per cent for two year olds which is OK. But in some pockets of towns there will be a collection of mothers where their children will not be immunised and if they come into contact with other children they will not be immune.
"The three cases we have are reasonably well and have not been hospitalised."
Another measles outbreak was reported in London last week where MMR immunisation rates are below 75 per cent in some districts.
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