Low immunisation rates are being blamed for a massive spike in mumps cases in Auckland.
There have been 300 cases in Auckland since January - more than the last 16 years combined. In 80 percent of the cases, the patient wasn't fully vaccinated.
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The Auckland Regional Public Health Service says part of the reason for the spike can be attributed to campaigns against immunisation, which have been scientifically discredited.
Ten to 29-year-olds are most at risk from the disease, which has fever-like symptoms as well as puffy cheeks and a swollen jaw.
In rare cases, complications can cause permanent hearing loss, and infertility in men. It can also cause miscarriages in non-immune pregnant women in the first three months.
People who aren't sure if they or their children have missed an immunisation should check with their GP.
The measles, mumps and rubella (MMR) vaccination is free to anyone who hasn't had both doses.