Canterbury GPs are having to turn patients away who aren't a priority for the measles vaccine, as the region's outbreak spreads to Dunedin.

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Authorities are scrambling to trace nearly 50 people who've been in contact with two people - a university student, and a person in their 30s - who've contracted measles in Dunedin.

There are two separate cases in Auckland that aren't believed to be linked.

The number of confirmed cases in Canterbury remains at 28, with 12 under investigation.

The immediate priority group is now those aged for those aged between 12 months and 13-years-old who have never been vaccinated.

GP Dr Phil Schroeder of the Canterbury primary response group told Checkpoint there was a "sigh of relief" when an extra 18,000 doses of the MMR vaccine arrived.

"We are now able to vaccinate as per the new priorities."

"It's awkward and difficult" to turn down those who didn't fall in the priority group, he said.

"But I think this is part of the bigger picture that we must protect those that are most vulnerable."

The primary response group hoped to vaccinate 100,000 people over the coming weeks with the MMR vaccine to control the spread.

Canterbury medical officer of health Dr Ramon Pink said people born after 1969 who had never been vaccinated, or who have measles-like symptoms, should stay away from gatherings or events.

The symptoms of measles include a cough or runny nose, conjunctivitis, a fever above 38.5C, and a rash.

"Measles is a very serious illness and the only way to prevent its spread is immunisation," he said.

"We have enough vaccines to immunise those who need it most - people aged between 12 months and 28 years who have never been immunised."

Dunedin asked to be careful

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People in Dunedin are being urged to check whether they are fully immunised against measles after two cases were confirmed in the city.

One was a university student and the other a person in their 30s, both who had travelled from Christchurch.

Dunedin medical officer of health, Marion Poore, was encouraging adults to ensure they have had two doses of the MMR vaccine.

The Canterbury outbreak led to Crusaders captain Sam Whitelock warning fans to think twice about going to this weekend's Super Rugby clash in Dunedin if they're feeling sick.

Mr Whitelock said he was up to date with his immunisations but he'd encourage anyone with health concerns to get checked out by their doctor.

Make vaccination 'compulsory'

High-profile GP Lance O'Sullivan renewed calls for compulsory vaccinations saying parents who didn't comply should pay more tax or have their benefits docked.

"We fine people for other things that even more trivial," he told Checkpoint citing the "seatbelt law".

"The protection offered by immunisation is far greater, yet we don't' make it compulsory."

He said the anti-vax lobby was loud and misinformation had caused people to die.

"We are going to see children die from vaccine-preventable diseases."

Measles facts: