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New Zealand's true vaccination rate is about to be revealed as lower than previously trumpeted, with the Ministry of Health's maths under review by Stats NZ.
The ministry is confident that the national vaccination rate will hold above 90 per cent once Stats NZ includes those who didn't qualify for the dataset used to make calculations. But it is expected it will not stay at the 96 per cent rate that the Ministry and Government ministers currently promote.
The dataset under scrutiny is called Health Service Utilisation 2020 and captures those who used the health system in 2020 with an age cut off at June 30 that year.
It means the vaccination rate for New Zealanders aged over 12 is calculated on those who were that age prior to June 30, 2020, and only if they had accessed health services.
The Herald has learned statisticians have pushed the Ministry of Health to use a dataset that has a better capture of the entire population but it maintains HSU 2020 gives an accurate picture of the population.
There has been pressure particularly from those working in Māori health because HSU 2020 is known to undercount Māori.
It's a criticism endorsed by the Waitangi Tribunal's finding in December that the Ministry of Health's data collection "does not collect sufficient data to accurately and equitably inform the rollout of the vaccine for Māori".
Stats NZ Manager of population estimates and projections Hamish Slack said it was "currently reviewing the Health Service User population" after the Ministry of Health requested a peer review.
He said the work had begun in March and was expected to be published on the Stats NZ website in early June.
NZ's true vaccination rate is about to be revealed as lower than previously trumpeted. Photo / Michael Craig
The review would assess "strengths and limitations" of the data set and make "suggested improvements and developments".
Covid-19 Minister Chris Hipkins was aware of the Stats NZ review and was confident it would keep the rate above 90 per cent with about 4m vaccinations administered across the population.
"I'm confident that with the ministry's use of HSU data plus its other outreach efforts that a very high proportion of New Zealanders are fully vaccinated with the primary vaccine course of two doses, and that this is well in excess of the 90 per cent target for everyone over 12. This is reflected in ... around 4m vaccinations administered against estimated population."
Work by the Herald's data team in early May showed the HSU data had partial vaccination at 96.4 per cent of people aged 12-plus and full vaccination at 95.2 per cent of people for those aged 12-plus.
When Stats NZ's December 2021 population estimates are used, the percentages came out significantly lower with 93 per cent of those 12-plus partially vaccinated and 91.8 per cent aged 12-plus fully vaccinated.
If the whole population was taken into account — that's including children under 5 years — then 84.2 per cent are partially vaccinated and 80.4 per cent are fully vaccinated.
Independent researcher Dr Rawiri Taonui. Photo / Mark Mitchell
Work by independent researcher Dr Rawiri Taonui aimed to compensate for HSU 2020 deficiencies when working out the Māori vaccination rate across DHBs. By his count, only Auckland and Canterbury show Māori above 90 per cent, compared to Ministry of Health statistics which show nine DHBs hitting the Māori vaccination target. Hipkins said Ministry of Health data showed — as of May 16 — 91.3 per cent of Māori aged 12 years and over were partially vaccinated and 88.3 per cent are fully vaccinated. He said: "Of course, we want that number to be higher, which is why we have 63 Māori providers across New Zealand working in their communities to ensure that accessibility is not an issue."
The Ministry of Health said it had asked Stats NZ to review its use of the HSU 2020 dataset and was expecting a report supporting its "confidence that a very high proportion of New Zealanders are fully vaccinated" with two doses — "well above the 90 per cent target".
"We believe this assertion will be supported by the Stats NZ review and report which is currently being finalised and will be made available shortly."
Otago University epidemiologist Professor Michael Baker said the lack of consistency across datasets was "a real problem". "If you have a service you want to deliver to 'everyone', you have to agree what 'everyone' is. If you're not measuring what you think you're measuring, we've got a problem. It's fundamental to running a vaccination programme to know your coverage."
Baker said New Zealand's vaccination coverage wasn't high enough with particular weaknesses in two areas. He said the slow progress of the third jab — 72.6 per cent overall but 55.9 per cent for Māori — was concerning. And the 25 per cent full vaccination rate for children aged 5-11 years was also a concern given the way schools had emerged as vectors for transmission.
