The school holidays could see fresh measles cases popping up around New Zealand as parents take their kids travelling, public health authorities have warned.

Between January 1 and September 26 there have been 1498 confirmed cases of measles notified across New Zealand, according to the Ministry of Health, with 1246 cases occurring in Auckland.

One in every three people with measles has been hospitalised - twice the usual rate.

The bulk of cases were still in South Auckland and predominantly among under-5s and 13-to 29-year-olds, Auckland Regional Public Health's medical officer of health Dr William Rainger said at a briefing on Thursday afternoon.

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The highest occurrence of measles in one week was in late August with 151 new cases, compared with last week's 133.

But because measles had a two-week incubation period, it was "too soon to say" if the outbreak had peaked, Rainger said.

"We are cautiously optimistic at this stage."

School holidays start on Saturday so the disease won't be spreading in the classroom over the next fortnight, but Rainger said parents may be travelling with their children.

"There could be some transmission for people who are incubating now to other parts of the country."

If they spread the disease to people outside Auckland it would be several weeks before those new cases were notified.

The bulk of measles cases continue to be in Counties Manukau DHB area in Auckland. Image / Auckland Regional Public Health Service
The bulk of measles cases continue to be in Counties Manukau DHB area in Auckland. Image / Auckland Regional Public Health Service

A parent who thought their child might be developing measles should call ahead to their doctor or healthline and get advice, and try to avoid spreading it further, he said.

Parents were encouraged to get their under-5s vaccinated because there was now sufficient measles vaccine to meet demand for groups the Ministry of Health had prioritised, Rainger said.

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"We know they're the group of people most badly affected and the ones that can get most unwell."

The ministry's priority is for all children to get their vaccines on schedule at 15 months (12 months in Auckland) and 4 years.

In addition, health authorities have been told to target those aged 15-29 years and Pacific peoples because they were the groups most affected by the Auckland outbreak.

However ongoing MMR shortages have led to claims some children are missing out on the vaccine.

Fresh stocks of 52,000 doses arrived in the country last week and another 100,000 have been secured, to arrive in coming months.

But adults over 30 have been told they will have to wait to be vaccinated due to "unprecedented demand".

Asked whether health authorities should have had more measles-mumps-rubella vaccine on hand to start with, Rainger said it would have been very difficult to predict demand.

In 2011's outbreak there had been 490 cases, and 112 in 2014.

"The size of the outbreak this time was very difficult to predict because we don't have an accurate estimate of the number of vulnerable people. It's easy to look back and say it would have been good to have more vaccine on hand."