Reduced mortality in New Zealand during the COVID-19 pandemic

New Zealand has had low case rates, hospital admissions, and deaths from COVID-19.¹ Stringent public health interventions (eg, compulsory self-isolation following travel, early border closure, nationwide lockdown, and isolation of cases and close contacts) were instituted in week 12 of 2020 (ie, March 16–19, 2020). Combined with its geographical isolation, these interventions meant that New Zealand eliminated COVID-19 in week 24 (ie, June 8, 2020),¹ although there have been subsequent cases due to border incursions.

To investigate the temporal association between these public health measures and all-cause mortality, we compared weekly death rates from 2015 to 2020 (appendix p 1) using data from Stats NZ Tatauranga Aotearoa. Reported weekly all-cause mortality in 2020 was similar to mortality in 2015–19 until week 17 (ie, the fifth week of public health measures) when mortality fell below historical rates, a trend which is still evident at week 42. There were a total of 25 deaths from COVID-19 from the start of the pandemic in New Zealand to week 42.

Interpretation of these time trends is limited by an absence of data on specific causes of death, due to coding delays and coronial inquiries. However, several important observations can be made. First, according to data collated in The Economist, New Zealand's reduction in mortality contrasts with the international experience of excess mortality during the COVID-19 pandemic. Second, the reduction in deaths is substantive. Across weeks 13–42 (ie, during and after lockdown), the mean weekly death rate was 11% lower than in 2015–19 (123·4 deaths per million population vs 138·5 deaths per million population, p<0·0001). The same pattern exists when compared with historical mortality rates from the longer period of 2011–19 (appendix p 2). Third, the reduction in all-cause mortality became apparent in week 17, after 5 weeks of lockdown, and remained below historical levels despite public health restrictions easing, during a period that is usually marked by an increase in all-cause mortality due to seasonal influenza and pneumonia. This continued reduction might be primarily due to the absence of an influenza epidemic in New Zealand in 2020 (appendix p 3), presumably because of public health measures that were introduced to stop the spread of COVID-19.²

However, alternative factors, such as fewer deaths from road traffic accidents, occupational causes, air pollution, and postsurgical complications, might also have had a role in the reduction of all-cause mortality,³ although these effects would often manifest during, rather than after, a strict lockdown. Finally, potential late adverse effects on mortality, resulting from reduced access to health care, have not become apparent.

As the costs and benefits of strict public health measures are debated, New Zealand's low all-cause mortality during this period is a striking observation. Further research, including monitoring of all-cause and disease-specific mortality in different countries, is needed to better understand the direct effects of COVID-19 and the measures that can be taken to reduce its burden.