The Ministry of Health has written to school principals advising them to ensure all pupils, parents and staff are immunised against measles as an outbreak threatens to sweep the country.
One senior medical officer is also warning New Zealanders aged between 17 and 23 are at risk because of a change in vaccinations 13 years ago.
The letter has gone to every school and preschool in the country in a bid to stem the contagious disease.
There have been 79 confirmed cases of measles since December - 59 in Auckland, 15 in Bay of Plenty, three in Wellington and two in Hawke's Bay. More than half of Auckland's cases are senior pupils at Westlake Boys High School.
Director of public health, Dr Darren Hunt, has asked schools to update registers to readily identify any unimmunised children in contact with measles.
Guidelines had also been issued, including separating unwell children while waiting to be taken home and keeping students and staff off school for 14 days.
"It's a highly infectious virus and so we know the potential is always there [to spread] so we're trying to get ahead of it," said Hunt.
Hunt said most cases were linked to international travel.
"What we're worried about and what we're trying to prevent is [infections] going further than just those direct contacts of people who are travelling," said Hunt.
The majority who had fallen ill were not immunised, he said.
The best protection against measles was the measles, mumps and rubella (MMR) vaccine which was free for all children and scheduled at 15 months and 4 years.
Auckland Medical Officer of Health, Dr Catherine Jackson, said older teenagers and young adults were falling ill which coincided with a change in the measles schedule in 2001.
This may have confused parents over whether their children had received their second dose, which changed from 11 years to four years.
A number of those aged between 17 and 23 years who had contracted measles in this latest outbreak had only received one dose of the MMR vaccination, she said.
Measles symptoms include fever, cough, red eyes and a runny nose, followed by a rash which tends to start on the face, before moving over the head and down the body.