Covid 19 Delta outbreak: How the Herald's Covid 19 vaccine tracker works

As New Zealand pushes for vaccination coverage of at least 90 per cent to protect against the spread of the Delta variant, the Herald's daily vaccination tracker has become a vital tool for understanding our progress. Data specialist Chris McDowall, who developed the tracker, explains how it works, where the numbers come from and why 90 per cent has become such an important benchmark.

Why vaccinate 90 per cent of the population?

The director general of health and the Minister of Health have advised that Aotearoa New Zealand needs a vaccination coverage of at least 90 per cent to keep our population safe and avoid future level 4 lockdowns.

The 90% Project is an NZ Herald initiative that aims to reach all New Zealanders to get the word out about vaccination so we can save lives and restore freedoms.

What's the difference between a third dose and a booster?

Some severely immunocompromised individuals might need a third dose of the vaccine to produce a sufficiently strong immune response. While this is a third dose for them, it is not the same as a booster.

How does the tracker count the number of people vaccinated?

Covid-19 vaccination sites provide information about every vaccine dose administered to the Ministry of Health. The ministry records this data in the Covid-19 Immunisation Register.

The ministry provides two sets of vaccination numbers from this register. One is an "operational" view, which counts the doses of vaccine being delivered, while the "person" view counts the number of people who are vaccinated. The two numbers are different, as some people will have been vaccinated overseas, or due to errors in data entry.

Our tracker uses data from the operational view, as it is currently the only publicly available source of data on boosters. This may result in slightly different numbers from what is published elsewhere.

How does the tracker count the eligible population?

Everyone in Aotearoa New Zealand aged 12 and over is eligible for the Covid-19 vaccine. The NZ Herald Vaccine Tracker uses totals from the Ministry of Health's Health Service User (HSU) database to estimate the size of this eligible population. These statistics are available in the "Details of vaccination data" spreadsheet linked from the bottom of the ministry's vaccine data page.

The HSU provides information about the number of people in New Zealand who used health services in 2020. The Ministry of Health advise using this database when calculating vaccine coverage. The NZ Herald's use of the HSU ensures consistency between the numbers we report and those on the Ministry of Health website.

The HSU is not based on the New Zealand census, which is administered by StatsNZ. Census-based population estimates and the Ministry of Health's HSU provide similar, but not identical totals. For that reason, we provide an alternative view of the tracker below based on the mid-2021 StatsNZ estimates.