Students at Auckland Girls' Grammar who aren't immunised against measles are being told to stay home.
Three cases have been confirmed at the central city school.
Medical Officer of Health Dr Richard Hoskins says none of those students had been immunised.
"We would classify the first one, which before the holidays, middle of July, as a what we call a community sporadic case which means we don't know where we got it from," he says.
Mr Hoskins thinks it's likely the other two cases were from exposure to that case.
