Background. The excess mortality rate in Aotearoa New Zealand during the Covid-19 pandemic is frequently estimated to be among the lowest in the world. However, to facilitate international comparisons, many of the methods that have been used to estimate excess mortality do not use age-stratified data on deaths and population size, which may compromise their accuracy. Methods. We used a quasi-Poisson regression model for monthly all-cause deaths among New Zealand residents, controlling for age, sex and seasonality. We fitted the model to deaths data for 2014-19. We estimated monthly excess mortality for 2020-23 as the difference between actual deaths and projected deaths according to the model. We conducted sensitivity analysis on the length of the pre-pandemic period used to fit the model. We benchmarked our results against a simple linear regression on the standardised annual mortality rate. Results. We estimated cumulative excess mortality in New Zealand in 2020-23 was 1040 (95% confidence interval [-1134, 2927]), equivalent to 0.7% [-0.8%, 2.0%] of expected mortality. Excess mortality was negative in 2020-21. The magnitude, timing and age-distribution of the positive excess mortality in 2022-23 were closely matched with confirmed Covid-19 deaths. Conclusions. Negative excess mortality in 2020-21 reflects very low levels of Covid-19 and major reductions in seasonal respiratory diseases during this period. In 2022-23, Covid-19 deaths were the main contributor to excess mortality and there was little or no net non-Covid-19 excess. Overall, New Zealand experienced one of the lowest rates of pandemic excess mortality in the world.

翻译：背景：在Covid-19大流行期间，新西兰的超额死亡率常被估计为全球最低水平之一。然而，为便于国际比较，许多用于估计超额死亡率的方法未采用按年龄分层的死亡与人口规模数据，这可能影响其准确性。方法：我们采用准泊松回归模型分析新西兰居民月度全因死亡数据，控制年龄、性别和季节性因素。模型基于2014-2019年死亡数据进行拟合，通过比较2020-2023年实际死亡人数与模型预测值估算月度超额死亡率。我们对拟合模型所用的大流行前数据时长进行了敏感性分析，并将结果与标准化年死亡率的简单线性回归模型进行基准比较。结果：我们估计新西兰2020-2023年累计超额死亡人数为1040人（95%置信区间[-1134, 2927]），相当于预期死亡率的0.7%[-0.8%, 2.0%]。2020-2021年超额死亡率为负值。2022-2023年出现的正向超额死亡率在规模、时间分布和年龄结构上与确诊的Covid-19死亡数据高度吻合。结论：2020-2021年的负超额死亡率反映了该时期极低的Covid-19感染水平及季节性呼吸道疾病的显著减少。2022-2023年间，Covid-19死亡成为超额死亡率的主要贡献因素，非Covid-19超额死亡率接近或等于零。总体而言，新西兰经历了全球大流行期间最低的超额死亡率水平之一。