Canterbury residents are being warned against an outbreak of measles with health officials saying that "vaccine mistrust is only one piece of the puzzle".

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Adults and children who have only had one dose of the vaccination could still be at risk and are among those now being prioritised at general practices for immunisation.

In less than two weeks at least 15 people have contracted the potentially life-threatening disease. And with more unconfirmed cases the district health board is predicting that number to rise.

The health board has been advocating for immunisation as people's best form of protection.

Director of the Immunisation Advisory Centre Dr Nikki Turner said they're having to ship more vaccine from Auckland to Canterbury to cope with a subsequent surge in demand.

In two days about 1800 vaccinations were distributed in the region, the equivalent of a month's supply, which Dr Turner said was a "positive sign."

"This is a really useful reminder to many of us that we may have missed out on our vaccines when we were young, or we may not have got enough to protect us," she said.

But Dr Turner and the health board said not all those contracting the disease were doing so because they'd intentionally opted against vaccines.

A health board spokesperson said though none of the 15 confirmed cases were fully immunised, some were young children who could have already been up-to-date with their vaccinations.

They may have had the first, and most effective, of the two recommended measles vaccinations before the age of four but may have been too young for the second.

Due to the outbreak, the DHB has distributed new advice in a letter to schools, kindergartens and parents this week.

It said in an outbreak, an additional dose of measles vaccine could be given from six months of age. Babies immunised before they were 12-months-old would still need two doses according to the schedule, at 15 months and 4 years.

Andrea Teal from Rangiora First Learners Pre-School & Nursery said her colleagues and her were doing what they could to stay measles-free - getting booster shots themselves, checking the immunisation status of children, and ensuring the facility was extra clean.

And the health board is also warning a certain group of adults may also be at risk.

Between 1969 and 1990 it was standard practice for GPs to give out only one vaccination, which is now thought to provide 90 to 95 percent protection.

The health board said there was no harm in having an extra dose of the vaccine if people were unable to find their records.

Canterbury medical officer of health Dr Ramon Pink said people who thought they may have been exposed to measles or have symptoms should call their general practice first.

"Calls made to general practices after hours will be answered by a nurse who will advise you what to do and where to go if you need to be seen," he said.

Measles facts: