An outbreak of mumps in Auckland has spread to Dunedin, which is experiencing its first outbreak of the disease in years.

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There have been 12 confirmed cases of the disease in Dunedin in the past month.

Public health staff working at the Southern District Health Board say all but two of those arose in the last 10 days.

Southern District Health Board medical officer of health Naomi Gough said they believed the Dunedin cases had been brought back to the city from residents visiting Auckland and the Pacific, where there are outbreaks.

She said not all the Dunedin cases were linked, but it had spread, forcing authorities to change their tactics.

"Rather than focusing on intense, case-by-case investigations for all of those mumps notifications, because we know that it is now circulating through the community, what we are really focussing on is targeting those populations that we believe are at risk and vaccinating them prior to them becoming exposed."

Dr Gough said mumps, which is usually mild but can lead to complications, spreads in the same way as colds and flu.

Those who have had mumps before, or have had two doses of the MMR vaccine, were protected.

In Dunedin, most cases appear connected to the university and polytechnic student population, and Dr Gough said they were the focus.

"If they are not sure whether they're immune to mumps they're encouraged to get vaccinated. The MMR vaccine is free to anyone who needs it. If people are unsure whether they've had two [doses] or not there's no harm in getting a third."

Students, in the midst of mid-term exams, are being targeted with social media and other messaging encouraging them to be aware and check whether they have had two doses of the vaccine.

A clinical group leader of student health at Otago University, Katherine Martin, said students were listening, and 150 vaccinations had been given in the past three weeks.

And 36 doses were given yesterday at a special clinic for Pacific Island residents in the city.

At the Auckland Regional Public Health Service, clinical leader Julia Peters said that was important, as Pasifika who have had been vaccinations may still remain unprotected.

"We know that in some Pacific countries the vaccination does not include mumps. It is a measles/rubella vaccination so people may think they've received MMR but they haven't."

Dr Peters said the outbreak underway in Auckland since the beginning of the year was not letting up, with cases still rising.

Late yesterday, there were 260 confirmed and probable cases in the region.

"The volumes we're seeing exceed the combined volumes we've seen in the last 12 years before this started," Dr Peters said.

She said young people between 10 and 19 were most affected, with "sub-optimal" vaccination rates in that group.

Mumps is a highly infectious viral illness spread in the same way as colds and flu and the MMR vaccine is free.