Estimating excess mortality during the Covid-19 pandemic in Aotearoa New Zealand: Addendum

In our previous article, we estimated excess mortality during in Aotearoa New Zealand for 2020 to 2023. Since our work was published, updated population estimates have been released by Statistics NZ. In this short letter, we provide the results of applying our original model to the new population data. Our updated excess mortality estimate of 2.0% (95% CI [0.5%, 3.3%]) is 1.3 percentage points higher than our original estimate because the new population estimates for the period 2020 to 2023 are smaller, but the main conclusions of our original article still apply.

💡 Research Summary

This short addendum updates the excess mortality estimates for New Zealand during the COVID‑19 pandemic (2020‑2023) by applying the authors’ original statistical models to the latest resident‑population estimates released by Statistics NZ. The original study (Plank et al., 2025) used the 2018 census‑based population series and a six‑year pre‑pandemic baseline (2014‑2019) to fit a quasi‑Poisson regression (QPR) and a standardized‑mortality‑rate linear regression (SMR‑LR). Expected deaths were projected for 2020‑2023, and excess deaths were defined as the difference between observed all‑cause deaths and these expectations.

Since publication, Statistics NZ has rebased the population series on the 2023 census and post‑enumeration survey. The new series shows a modest overall decline of about 0.9 % (≈44,500 people) for the period ending 30 June 2023, with the most pronounced reductions in the 90 + age group. Because expected deaths are a function of the at‑risk population, the smaller denominator lowers the expected death count and consequently raises the excess‑mortality proportion.

Re‑running the original QPR model with the updated population yields 2,849 excess deaths (95 % CI