Unvaccinated children in Auckland should still return to school today despite the measles outbreak continuing, health authorities say.
Counties Manukau is the hardest hit with 23 new cases in the week ending 12 July.
About 50 schools and early childhood centres in Auckland have been affected and authorities are pushing vaccinations in a bid to curb the increasing rates of the disease.
There had been 227 reported cases of measles in the Auckland region so far, 125 of those in the Counties Manukau area, Auckland Regional Public Health's Julia Peters said.
The numbers were increasing with, on average, six new cases being reported each day.
About 50 schools and early childcare centres had been affected across Auckland, Dr Peters said.
"Not all of those are in South Auckland, but a high proportion are so we are obviously working closely with those institutions to help them contain the outbreaks."
She said schools knew which of their students and staff were not vaccinated, and those people could be told to stay home if there was a case of measles at the school.
Parents with vaccinated children should feel safe sending their kids to school or day care.
"One MMR [measles, mumps and rubella] vaccine provides excellent protection against the measles.
"Obviously, we would like to see people have two, so the first one at 12 months and the second one at four years, but one vaccination, from our perspective, provides sufficient immunity."
Children under the age of four, and people in the 19-24 age bracket had been the hardest hit, Dr Peters said.
Immunisation Advisory Centre director Nikki Turner said there needed to be a more systematic approach to making sure everyone had been vaccinated.
"Measles is one of the most highly contagious viruses we have in the world. If the measles virus continues to meet people who are unvaccinated it will continue to spread.
"[It] is directly related to whether we have enough vaccinated people to prevent the spread."
How safe it was for unvaccinated kids to go to school depended on the numbers, Dr Turner said.
"If you had a very large percent of unvaccinated children then the school would be at risk - remembering our young children have got very high vaccination rates."
Adults who were not sure if they had been fully vaccinated needed to check their immunity.
Counties Manukau District Health Board's Gary Jackson said measles was not the only illness causing concern this winter.
"One is our more general respiratory infections which are relatively high for this time of the year, particularly influenza."
Dr Jackson reiterated the message that measles vaccination was crucial and health authorities were trying to get more people immunised.
For babies, the age of first immunisation has been dropped from 15 months to one year.
Dr Jackson said the outbreak had not spreading as fast as previous ones, which suggested vaccination levels were higher.