The number of measles cases confirmed in Canterbury today remains at 28.

Forty-seven cases of the measles had been confirmed in New Zealand this year as of yesterday, according to figures from the Immunisation Advisory Centre.

The Canterbury outbreak made up the bulk of them with 28 confirmed cases while 12 had been reported in the Waikato, three in Auckland, two in the Bay of Plenty and one in both Counties Manukau and Otago.

Seven people in Canterbury had been hospitalised and two needed treatment in the intensive care unit. The outbreak started on February 22.

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Canterbury medical officer of health Ramon Pink today said there had been no increase in confirmed cases in the last 24 hours. There were 12 possible cases under investigation.

"The fact we haven't seen a significant rise over the last 24 hours is encouraging," he said.

He said the majority of those who had contracted the disease were unvaccinated although six people had received one dose of the vaccine while four people had both the recommended doses.

He stressed getting the disease after having two doses of the vaccine was the exception, not the norm.

Auckland Regional Public Health Service acting clinical director Dr William Rainger said there had been no new reports of measles in Auckland since yesterday's announcement two cases had been confirmed.

He said they were aware one of the people had recently travelled overseas to a country affected by a measles outbreak making it likely the illness was contracted during the trip. The source of infection of the other person was unknown.

Even though measles has been considered eradicated in New Zealand since 2017, every year there are a number of small outbreaks started by someone bringing the disease back from overseas.

Otago University Professor Michael Baker, who is based in Wellington, said experts believed that until 95 per cent of the population was immunised small outbreaks would continue to occur.

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Rainger warned though, that it could take up to two weeks for people to have a "good immune response to the vaccine" so people needed to be careful and remain vigilant during that time.

The last big outbreaks in New Zealand were in 2011 when two separate outbreaks saw 595 people fall ill.

Although no one has died from measles in New Zealand since 1991, it was a serious disease with one in 10 people needing hospital treatment. The most serious cases could result in deafness or swelling of the brain.

Under-immunised people who came within two metres of an infectious person, however briefly, had a 90 per cent chance of contracting measles.

Pharmac director of operations Lisa Williams said national stocks of the measles, mumps and rubella (MMR) vaccine was at normal levels for this time of year.

New Zealand usually used about 12,000 doses per month and Pharmac always had three months' supply in its national store.

About 32,500 doses had been delivered to and distributed in Canterbury since March 6 but the region's vaccination programme would have no impact on stock levels for the normal childhood immunisations, she said.

About the vaccine
The measles vaccine was introduced to New Zealand in 1969 and was replaced by the MMR vaccine in 1990.

Anyone born prior to 1969 is considered immune to measles because there was no vaccination until then and the disease is so highly infectious they would likely have already contracted it if they were susceptible.

Up until about 1990 it was common practice for people to only get one dose of the measles vaccine so anyone born between 1969 and 1992 will probably only have had one shot.

Rainger said a single dose of the MMR vaccine was 95 per cent effective in preventing measles and two doses was 97 per cent effective.

Director of Massey University's Infectious Disease Research Centre Professor David Hayman said there were a number of reasons the vaccine might not work.

The vaccine may have given when the person was already infected, the person may have been immunised to young or records could be incorrect.

"Typically, most people who don't respond to the first vaccine dose will respond to the second dose, which is why two doses are recommended."

A study carried out by Hayman and published in 2017 found 82.8 per cent of measles cases in the country between 2007 and June 2014 were in unvaccinated people. Of the rest, 12.6 per cent had received their first dose and 4.7 per cent had received two doses.

The figures were higher than the typical statistics but the team had no information about the patients so could not confirm why.

The two doses were available free to New Zealanders who had not had them both, although practice nurse fees may apply.

Immunisation rates
Baker, who is based in Wellington, said vaccination rates around the country were very similar, meaning an outbreak similar to that seen in Canterbury was possible in any region.

At the end of last year, 88 per cent of 5-year-olds in New Zealand were fully vaccinated against measles, mumps and rubella, Baker said. The rates in the Auckland and Canterbury district health boards were similar at 87 per cent and 92 per cent respectively.

The lowest rates were in the West Coast with only 70.5 per cent and in the Bay of Plenty with 78 per cent. The rest of the country sat between 83 per cent and Canterbury's 92 per cent.

"Measles is an infectious agent that will always find a gap if there is one," he said.

What to do
In Canterbury, the focus was on vaccinating people between 12 months and 28 years old who had never been immunised.

Over time, access would be expanded to more groups.

There was no immediate threat in other parts of the country but anyone who had not received two doses was encouraged to get up-to-date.

How serious is measles?
Measles is a serious illness. One in 10 people with measles need hospital treatment and the most serious cases can result in deafness or swelling of the brain.

Measles is one of the most infectious airborne diseases and a person is contagious before the rash appears. It is very easily transmitted from one person to another, possibly by being in a room where an infected person has been.

I'm about to travel to a country that has a measles outbreak. What should I do?
The Ministry of Health is advising anyone travelling overseas to be up to date with their MMR vaccinations. In addition, the Ministry recommends that infants aged 6-15 months travelling to countries where there is a current measles outbreak be given MMR vaccine before they travel. This is an additional vaccination for those infants – they will still need their usual MMR vaccinations at 15 months and four years old.

What are the symptoms of measles?
Measles symptoms include a high fever, runny nose, cough and sore red eyes, followed by a rash starting behind the ears and spreading to the body a few days later.

How can I protect myself and my family against measles?
The best way to prevent measles is to be immunised on time, with two free MMR vaccinations for all children at 15 months and four years. Two doses of MMR vaccine are at least 97 per cent effective in preventing measles.

What does MMR stand for?
MMR stands for measles, mumps and rubella, as the MMR vaccine provides protection against all three of these illnesses.

I don't know whether I've been immunised or not. What should I do?
If you are not sure how many doses you have had, talk to your doctor as the information may be in your medical records. You may also have your own health records e.g. your Plunket or Well Child/Tamariki Ora book. If it's unclear whether you are immune, or whether you've had two doses, vaccination is recommended. Check with your GP first as in some instances, such as pregnancy, you should not be immunised.

If I've been in contact with someone with measles, how long will it be before I know if I've caught it?
It usually takes 10 to 14 days for someone who has caught measles to start showing symptoms.

Are there sufficient supplies of MMR vaccine?
Auckland Regional Public Health Service isn't aware of any vaccine supply concerns for the Auckland region.

Where can I seek advice or find out more about measles?
For more information or advice on measles, please call Healthline on 0800 611 116 or see the Ministry of Health's measles page.