Health authorities in Canterbury have ruled out the possibility that a defective vaccine could be behind several cases of measles in immunised children.
Canterbury District Health Board has confirmed seven more cases, bringing the number to 39 since the outbreak began last month. Another 23 children are thought to have the illness.
Five of those who have fallen ill have been hospitalised.
The affected pupils come from a total of seven high schools, four intermediate schools, seven primary schools and nine early childhood centres.
The district health board is investigating why some of the children fell ill despite being immunised.