An outbreak of measles in Waikato may take two or three weeks to get under control, a health expert says.
The Waikato District Health Board has ordered a college to close, and its 700 students and staff will have to prove they have been vaccinated for measles - or they won't be allowed back on school grounds.
In a letter sent to parents on Friday, Morrinsville College acting principal Scott Jenkins confirmed a student had contracted measles and the school would be closed today.
The board's medical officer of health, Richard Wall, said those who had not been vaccinated must stay at home and not return to the school until 24 May.
The school will reopen tomorrow to those who can provide written evidence they had been given two MMR, or measles vaccinations.
Bronwyn O'Sullivan has a child at Morrinsville College and said the measles case was a reminder of the need to stay up to date with vaccinations to keep children healthy.
One of her children had accidentally missed her second booster shot but received it this morning.
Ms O'Sullivan said the school had responded brilliantly by following the instructions of the Medical Officer of Health when a student at the school was confirmed to have measles.
She said she had not heard of any parents at the school who did not want their children vaccinated.
Michael Baker from the Department of Public Health at Otago University told Morning Report the school was doing the right thing to try to limit the outbreak.
"Measles is a serious illness, one in 10 people who get infected will go to hospital, and people may get encephalitis, pneumonia, middle-ear damage ... it's the most infectious disease we know of," he said.
The disease has an incubation period of about 10 days, so it will take two to three weeks see what will happen with this epidemic, he said.
Acting Principal Scott Jenkins said there has been a positive response to the steps the school has taken after a student was confirmed to have measles.
He said parents were aware there was a wider collective responsibility to ensure the safety of students, and staff were also acting responsibly.
"There's been a lot of teachers racing around over the weekend and today getting shots and trying to find their documents.
"As you'll appreciate it's harder because of the long length of time and because some of our teachers come from overseas and they have to collect all of those aswell."
Mr Jenkins said he knows of only one parent who had contacted the school to say they would not be vaccinating their child.
Professor Baker said measles is very close to being eliminated in New Zealand but there may still be pockets of the community that are not vaccinated.
The health board said it was dealing with 20 confirmed cases of the measles, and another possible 12.