The characteristic rash caused by measles, on the cheek of a child infected with the virus, during an outbreak in the USA in 2024. Photo: Supplied/ US CDC
As many as 150 people a week could get infected with measles if an epidemic takes hold, in a "pessimistic" scenario, official measles modelling suggests.
Modelling to estimate the impact of a potential measles epidemic was done last year by the government-owned ESR, now known as the New Zealand Institute for Public Health and Forensic Science (PHF).
The pessimistic scenario described what could happen if the virus took off in unfavourable conditions, such as in a community with low vaccination rates.
However, it suggested any epidemic was more likely to look like the one in 2019, with a peak of about 100 cases a week.
Then, there were 2185 known cases, with 768 people hospitalised, about half of them children.
Health officials are currently trying to stamp out an outbreak, with 13 known cases across six regions centres, and 2142 people known to have been exposed.
They have warned the health system would struggle to cope with more than 100 measles cases a week if the current outbreak got out of control.
A summary of the modelling was included in measles advice given to Minister of Health Simeon Brown in May.
That advice noted there was a high degree of variability between the two scenarios, but considering a higher one would be useful for planning.
PHF's full report said the modelling used AI to create simulated populations and scenarios that ran over six months.
It could not predict exactly what would happen, but looked at how measles could spread in similar conditions to the 2019 outbreak, with the lowered 2024 childhood vaccination rates factored in.
It then looked at whether other variables would come into play, such as the outbreak taking hold in an area with particularly low vaccination rates, which could increase the rate of infection.
The modelling also found that increasing vaccination rates by five percent could halve the number of hospitalisations in an outbreak, but noted that had to be done quickly to be most effective.
PHF said the work was not a prediction or forecast. Instead, it looked at how scenarios might play out to help with planning a response.
Experts have been saying for some time an outbreak of measles was inevitable in New Zealand given waning vaccination rates.
There was a large cohort of young adults who likely missed out on getting the full dose of two jabs of the measles-mumps-rubella (MMR )vaccine in childhood, and current childhood rates have dropped to 82 percent for under-fives, and just 72 percent for Māori under-fives.
Coverage of 95 percent was needed for herd immunity, where those who were not vaccinated would also be protected.
'Entirely preventable'
Tairāwhiti Medical Officer of Health Dr Oz Mansoor told Morning Report about 500,000 people could be susceptible to measles.
He said the outbreak could be worse than the one in 2019 because vaccination coverage has dropped.
"The other aspect of what's going to happen is the vaccine uptake, because this is an entirely preventable condition.
"Unfortunately we are in a situation where coverage has not been so good, plus we have our young adults, so we do have quite a lot of measles susceptible - perhaps something around half-a-million or more people who are susceptible to measles - so that's where that potential for the very large outbreak that's been modelled."
The measles outbreak in 2019 infected more than 2000 people, with about a third being admitted to hospital.
There were currently 13 confirmed measles cases, with more than 2000 close contacts identified.
"It's like it's a fire ready to go, and I think we have eliminated measles - certified in 2017 by the World Health Organisation… and we've had a very aggressive response whenever we've had incursions because measles has been on the rise locally."
He said the vaccine is close to 100 percent effective after two doses, and while it was not perfect, anyone vaccinated was less likely to get severe disease and to pass it on.
"We're not yet close to reaching our 95 percent [vaccination] target, but we are doing our best.
"I think the problems we have with immunisation is a reflection of the challenges we have in our health system."
The Immunisation Advisory Centre's Dr Mamaeroa David told Morning Report that adults who are not sure whether they've been vaccinated or twice, should go and get the jab.
The centre's senior Māori medical advisor said those born before1969 were likely to have good measles immunity.
"After 1969 there's a possibility that you only had one dose of MMR, which gives you a little bit of protection, but two doses gives you up to 98 percent or more, so it's very very effective.
"Adults are the people who pick up this disease and take it around to our babies, so that's why it's very important for adults to be protected."
David said the vaccine was not free for non New-Zealand residents who haven't been exposed to the virus.
She said people should see their GP or pharmacist if they wanted to get vaccinated.
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