Public health officials are bracing for more cases of measles after 20 students were struck down at Westlake Boys High School.
The school is telling students who have not been immunised to stay home to avoid the highly infectious illness spreading further.
Auckland Regional Public Health Services confirm there have now been 40 cases of measles in Auckland this year - half came from the North Shore school.
A spokeswoman says staff are also seeing a rise in cases spreading within the community.
"We are expecting more cases in Auckland including possibly more from Westlake Boys," she says.
More than 750 people have come into contact with people infected with measles during Auckland's latest outbreak.
The service has contacted these people asking anyone who is not immune to quarantine themselves at home.
There have been 58 confirmed measles cases nationwide since the end of December, according to the Ministry of Health.
This includes 30 new cases in Auckland this month alone.
Outside of Auckland, there were 14 cases in the central North Island, three in Wellington and one in the Bay of Plenty since the end of December 2013.
The initial measles outbreak originated in the Philippines, arriving in New Zealand via a hip-hop dance competition in Sydney.
"There is no treatment, and complications can be severe, including hospitalisation," service health medical officer Richard Hoskins says.
"The only way to prevent measles is to be vaccinated with two doses of the MMR vaccine."
Public health officials are working with Westlake Boys High School to stop the spread.
The school has distributed information in letters to students, their parents, staff and the board of trustees.
Westlake Boys High School declined to talk to the media regarding the outbreak and referred inquiries on to the health service.
Principal David Ferguson has written to parents asking all students who are not immunised to stay at home until March 8.
Parents with children suffering measles symptoms are advised to avoid busy GP waiting rooms and to call a doctor instead.
A measles outbreak in 2011 led to 600 people being infected nationwide including many who needed hospital care.
There are currently measles outbreaks in overseas countries including the Philippines, Australia, Europe, the United Kingdom, Asia, India and North America.
Fairfax NZ News
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