Covid-19: New study raises more worries over Māori vax estimates

Māori vaccination rates may have been sizably lower than those officially reported - raising fresh concerns over datasets the Ministry of Health has used to measure coverage. Photo / Sylvie Whinray

Māori vaccination rates may have been sizably lower than those officially reported – raising fresh concerns over datasets the Ministry of Health has used to measure coverage.

In a just-published analysis, researchers found how different ways of calculating the population sizes of ethnic groups could have a notable impact on vaccination rates – with implications for some of our most vulnerable communities.

To compare those vaccination rates, the team looked at Stats NZ's sub-population estimates for 2020, along with the ministry's Health Service Utilisation (HSU) dataset.

The HSU includes people who used health services that same year and formed the basis for official vaccination targets – including the symbolic 90 per cent threshold that was used to determine local public health settings around the country.

However, it's been repeatedly criticised as a flawed measure, given Māori were known to use healthcare services less frequently and, when doing so, sometimes identified as another ethnicity.

In their analysis, looking at coverage data from March to April, the study authors also defined risk based on factors such as age and the number of vaccinations people had received.

According to HSU data, there were approximately 718,948 unvaccinated residents, of whom 76 per cent were younger than 12 years.

While the roll-out achieved relatively high rates of coverage across most cohorts, their results showed the denominator mattered.

For instance, if Census data was used instead of HSU, the proportion of vaccinated Pacific females older than 25 would have risen by 6.3 per cent.

But at the same time, and more worryingly, the proportion of vaccinated Māori over 25 would have fallen by five per cent for females – and 12 per cent for males.

The study authors further pointed out that younger and marginalised populations were likely under-represented by HSU as they didn't frequently use health services - leading to over-estimates of coverage in these groups.

"However, if we use census data we may underestimate subpopulation sizes of Pacific peoples, which could lead to underestimates of unvaccinated, highlighting the difficulties in using census data to estimate accurate subpopulation counts in dynamic, migrant populations."

They concluded that, while true disparities in vaccinations remained unclear, ethnic minority groups should continue to be reached through targeted engagement.

"This is further evidence that the current way we do health statistics in this country aren't robust enough for an epidemic – and they aren't robust enough to inform timely responses to an epidemic," co-author and University of Auckland statistician Andrew Sporle said.

"We've known that for a while, but what's new about this particular study is it actually identifies the number of people at risk of a preventable, poor outcome from Covid.

"That's particularly important for South Auckland, where we're talking about priority populations which have been predicted – and demonstrated – to have worse outcomes."

The study, published in medical journal JAMA Network Open overnight, follows a Herald investigation into the issue – with experts suggesting inflated vaccination rates may have even led to higher rates of death and illness.

Some health statisticians told the Herald that the HSU – which Stats NZ has been reviewing the ministry's use of - may have undercounting Māori by as much as 20 per cent in critical age bands.

A ministry spokesperson acknowledged the new study – and also noted that any data set had limitations, "which has always been acknowledged by the ministry in the publication of its HSU data".

"This is why it is used in conjunction with a comprehensive range of sources to ensure the data is as robust as it possibly can be."

The ministry had continued to work to refine and improve the quality of its HSU data as the rollout had progressed, with Stats NZ's report soon to be published.

"Work is also underway to refresh our HSU dataset using the completed 2021 data, and we expect this to be published In line with our agreed HSU release cycle anticipated mid-year."

The spokesperson said we could still have confidence that "a very high proportion" of Kiwis were now vaccinated against Covid-19.

"This is because of the huge amount of work that has occurred across the motu by DHBS, health providers, the ministry and many others to vaccinate as many people as possible."