Estimating excess mortality during the COVID-19 pandemic in Aotearoa New Zealand: addendum

Our recent article [1] estimated the excess mortality in Aotearoa New Zealand between 2020 and 2023 by using official Statistics NZ estimates for the resident population based on the 2018 Census [2], which was the best data available at the time the research was carried out (November 2024). Since our study was published, Statistics NZ have released updated population estimates for 30 June 2018 onwards based on the 2023 Census and 2023 post-enumeration survey [3] (see Supplementary Material section 1 for details). This has enabled us to update our results by using the most up-to-date population data [4]. Due to intercensal discrepancy, the new population estimates for 2020–3 are lower than those used in our original study (Supplementary Fig. S1), with the largest percentage decrease occurring in the >90-years-old group (Supplementary Fig. S2). As a result, the expected deaths are lower and our updated excess mortality estimate is 1.3% points higher than that reported in the original article (see Table 1), although the 95% confidence intervals (CIs) are overlapping and the new central estimate is within the original CIs [1]. Our updated estimate for excess mortality of 2.0% (95% CI 0.5%, 3.3%) implies that we can be confident that more deaths occurred than would have been expected in the absence of a pandemic. However, this estimate for excess mortality remains low in comparison with many peer countries, which experienced excess mortality rates close to 10% [5]. Updated versions of the figures and tables that appeared in the original article are provided in the Supplementary Material. All the updated results used the same deaths data and the same computer code as in the original analysis. The data and code to reproduce these updated results are publicly available at [6]; the data and code used in the original analysis continue to be available at [7].