More than three-quarters of New Zealanders infected with measles have not been vaccinated.
The number of measles cases nationwide has risen to 67, with three more people confirmed to have contracted the potentially deadly disease in the last week.
The Institute of Environmental Science and Research report showed 52 of the 67 were not vaccinated.
Public health physician Dr Jill Sherwood said this was expected and while some cases are in vaccinated people, most of them have received only one dose.
Medical professionals continue to urge New Zealanders to get the MMR vaccination.
University of Auckland senior lecturer in vaccinology Dr Helen Petousis-Harris said getting people vaccinated was ultimately going to help stop future outbreaks.
"While it has been rough on general practices trying to meet the needs of people presenting for vaccination it is great to see so many people fronting up and getting up to date with their MMR vaccinations," Petousis-Harris said.
Outbreaks have been in Auckland and Canterbury.
Canterbury District Health Board last week announced they would be extending their vaccination campaign to a wider age group of people.
A second dose of the vaccine is being made available to those aged 12 months to 28 years, caregivers of infants aged up to 12 months and people who work with children aged 29 to 50 years.
The DHB was continuing to provide the vaccine to children and adults aged 12 months and 28 years who had never been vaccinated
Petousis-Harris said the current measles outbreaks was no bigger than previous outbreaks in the last few years.
"As it stands at the moment, 2009, 2011, and 2014 were significantly bigger.
"However, if we go back to the '90s we had a whopper in 1991 with thousands of cases and seven deaths and then managed to stave off another in 1997 with a mass vaccination campaign," Petousis-Harris said.
She said she did not think we would see another 1990s episode as we did not have enough susceptible people in the community.
"However, the current outbreaks indicate we still have some gaps to close and with the global resurgence of this disease we can expect more measles cases getting off a plane and walking through our communities," Petousis-Harris 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 were 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 been given when the person was already infected, the person may have been immunised too 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.
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?
MR 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 such as 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.