Auckland is in the midst of a full blown outbreak of the mumps, with more than 450 cases confirmed so far this year and the number rising daily.
The huge amount of cases means Auckland's had more than 16-years-worth of cases in just nine months.
"This is definitely a massive increase and can really only be described as a full blown outbreak that shows no sign of abating at the moment," Dr Julie Peters Clinical Director of Auckland Regional Public Health Service said.
The statistics are troubling, showing of the confirmed cases, 80 per cent aren't fully immunised, 60 per cent are aged 10 to 24 and 50 per cent are Pasifika.
"The outbreak started in west Auckland probably as a result of someone coming in to NZ who had been infected overseas.
"Now its spread across the region 40 per cent of the cases are in west and 40% are in south Auckland," Dr Peters told 1 NEWS.
With half the cases affecting Auckland's Pacific community, Dr Nikki Turner of the Immunisation Advisory Centre says many in the community won't have been vaccinated.
"Many people who were born in Pacific countries may have missed out on mumps vaccines. Some of the traditional ones didn't actually have mumps combined with measles," Dr Turner said.
Schools with confirmed cases of mumps are asking students who aren't fully vaccinated to stay home for almost four weeks
Health officials say everyone under 36 needs to make sure they're immunised which you can do for free with your GP.