As the number of measles cases climbs in Canterbury, schools and workplaces are scrambling to stay disease-free and protect those who could have been exposed.

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Twenty-five people had the disease as of Monday afternoon and the Canterbury District Health Board is warning that number will grow.

Yesterday Rangiora Borough School principal Alan Sutton had the difficult task of informing parents that their children may have been exposed to measles.

One of the school's students has been formally diagnosed with the highly contagious disease and there are at least 28 others at the school who are unimmunised.

Mr Sutton has contacted the families of the 28 unvaccinated students recommending that they get the two recommended MMR vaccines, or stay at home.

"Some (parents) have actually come in and said they are now going to immunise them, but what they have actually found out is that it is not that easy." said Mr Sutton. "Number one the supply and number two even if they do get vaccinated it takes 14 days to kick in anyway. Probably of that 28 we probably have 50 percent of those... for this week have chosen to stay at home."

At Fernside Preschool, near Rangiora, owner Nicola Baynes said there had been slightly less children attending sessions over the past two weeks because some families are choosing to self-isolate.

"We're definitely seeing a lot of children who are not here, because their parents are choosing to keep them at home until either they can get that vaccinations or the outbreak peters out. Probably between five and ten children are voluntarily not coming."

Kindergartens aren't allowed to separate or exclude unimmunised children but some are asking parents for their children's vaccination details.

Jeanette Allison owns Poppies Preschool in Christchurch and Peppertree Preschool in Rangiora and said it helps to know who is and isn't protected in case someone at the preschool is found to have measles.

"So we're just letting them know that if a child attends with measles then they will have to stay away, but at this stage we can't exclude them."

Education Minister Chris Hipkins said he has no plans to make vaccinations compulsory for children.

Photo: RNZ / Katie Todd

"Personally I think kids should be vaccinated," said Mr Hipkins, "but I'm not going to make it compulsory. I'm not going to say that kids should lose their right to an education because their parents don't choose to vaccinate."

The Christchurch court system has also now been exposed to the disease, with a police prosecutor diagnosed with measles.

The Law Society has issued a notice warning that the prosecutor will have had contact with many people in the period that they were infectious but was not yet aware that they had contracted the measles.

This includes all of the Christchurch prosecutors.

It said the extent of other contacts will likely be extensive and impossible to trace.

The Ministry of Justice has not been available for further comment today.

At Canterbury's biggest polytechnic, Ara Institute of Canterbury, there's been no measles cases, but the health centre is dealing with a huge influx of students seeking vaccinations.

The Ministry of Health has said two doses of measles vaccine provides the most effective protection, however between 1969 and 1990 it was standard practise to only provide one measles vaccination leaving around 100,000 people in need of updated shots.

Anyone born after 1 January 1969 can get the measles vaccine for free, however supplies of the vaccine are however in short supply, and GPs are prioritising people most at risk.