Herd immunity for measles in New Zealand may already have gone, the director of Public Health, Dr Caroline McElnay, says.
Speaking to Morning Report today she said: "For measles you need about 95 percent immunisation coverage for herd immunity and we don't have that. What we haven't yet lost is our elimination status for measles, which many other countries in the world are beginning to lose because measles is beginning to spread."
The country had at least six months to stop the outbreak before we lost elimination status, she said.
"If we have the same strain of measles circulating in New Zealand for 12 months then you are deemed to have lost your status, so for us that could be March (2019), it could be June, but March would be the soonest that that would happen."
Meanwhile, a vaccinologist is warning about the further spread of measles through a number of large school sports events due to be held soon.
Hundreds of students at Auckland's Manurewa High School have been sent home due to the outbreak, which has been confirmed in 13 students there.
About 850 cases have been reported so far this year - making it the worst measles outbreak in 22 years.
Manurewa High School is due to play St Thomas of Canterbury College in the Secondary Schools Rugby League Nationals on Monday, when a netball tournament for secondary schools in the North Island also begins.
And 11,500 students are due to take part in the Anchor AIMS Games in Tauranga from 8 September.
Dr Helen Petousis-Harris, a senior lecturer in vaccinology from the University of Auckland, said if any measles carriers took part in events the risk of infecting others would be greatly amplified.
"If somebody is infectious and going to a sports event where you've got lots of susceptible people then it's very likely that there will be further cases as a result of that," she said.
At Manurewa High School 300 students have been sent home after 13 confirmed cases at the South Auckland school, and students who haven't been vaccinated or can't prove they've been immunised are being made to stay home.
Julie Pukeroa is worried about what the outbreak is going to mean for her Year 13 daughter's upcoming dance assessment, for which she needs the credits.
"Half of her dance class were in the library on Wednesday morning and told to go home," she said.
"So the concern I have is if she's not there for that assessment tomorrow then does her partner miss out? Or if she goes and her partner's not there then does she miss out? Nothing's being said to us about how assessments are being handled at this time."
So far there have been 850 cases of the infectious virus across the country, with about one in three needing hospital attention.
The outbreak in Auckland is escalating, with more than a quarter of cases nationwide occurring in the city in the last two weeks.
It is the worst measles outbreak in 22 years, with most of the cases contained to Auckland at this stage.
There have been 230 cases of measles in Auckland in the last fortnight, and only 10 cases everywhere else in the country.