The number of children becoming susceptible to measles is growing by about 1000 a month, according to public health experts.

The figure has been highlighted in a briefing paper by the Public Health Communication Centre, a group of leading doctors and public health researchers.

Childhood immunisation rates are stuck on about 82 per cent, and for years have been below the 95 per cent needed for population-wide immunity.

That means the proportion of unimmunised people in the population is continuing to grow.

It has resulted in a vaccination rate so low in children under 8 that it has reduced the level of herd immunity which helped slow the spread of the last epidemic, in 2019, the briefing says.

Even then, hundreds of children were hospitalised.

Conditions are now "primed" for a big epidemic, the briefing authors say.

They are very similar to the big epidemics of the 1980s and 1990s, with the added danger that there are now more unprotected young adults.

Doctors at the centre renew their calls for an urgent school and preschool-based immunisation campaign, and checks at the border.

Health minister Shane Reti in January said he's increasingly worried about the possibility of a measles outbreak in New Zealand. Reti says immunisation has been identified as one of the government's health targets, and it will be a high priority.

Since then, pharmacists have been given the ability to vaccinate under-5s.

The government has not implemented pre-school vaccination programmes nor checks at the border.

Te Whatu Ora/Health NZ says it has said it had a national response plan ready to go if an outbreak occurred, including an incident response team, which was mobilised six times in 2023 because of cases which came over the border.

-RNZ.