Learning from the pandemic: mortality trends and seasonality of deaths in Australia in 2020

Aim To assess whether the observed numbers and seasonality of deaths in Australia during 2020 differed from expected trends based on 2015-19 data. Methods We used provisional death data from the Australian Bureau of Statistics, stratified by state, age, sex and cause of death. We compared 2020 deaths with 2015-19 deaths using interrupted time series adjusted for time trend and seasonality. We measured the following outcomes along with 95% confidence intervals: observed/expected deaths (rate ratio: RR), change in seasonal variation in mortality (amplitude ratio: AR) and change in week of peak seasonal mortality (phase difference: PD). Results Overall 4% fewer deaths from all causes were registered in Australia than expected in 2020 [RR 0 center dot 96 (0 center dot 95-0 center dot 98)] with reductions across states, ages and sex strata. There were fewer deaths from respiratory illness [RR 0 center dot 79 (0 center dot 76-0 center dot 83)] and dementia [RR 0 center dot 95 (0 center dot 93-0 center dot 98)] but more from diabetes [RR 1 center dot 08 (1 center dot 04-1 center dot 13)]. Seasonal variation was reduced for deaths overall [AR 0 center dot 94 (0 center dot 92-0 center dot 95)], and for deaths due to respiratory illnesses [AR 0 center dot 78 (0 center dot 74-0 center dot 83)], dementia [AR 0.92 (0.89-0.95)] and ischaemic heart disease [0.95 (0.90-0.97)]. Conclusions The observed reductions in respiratory and dementia deaths and the reduced seasonality in ischaemic heart disease deaths may reflect reductions in circulating respiratory (non-SARS-CoV-2) pathogens resulting from the public health measures taken in 2020. The observed increase in diabetes deaths is unexplained and merits further study.

Automated summary

This study aimed to compare the observed numbers and seasonality of deaths in Australia in 2020 with the expected trends based on data from 2015-2019. The results showed a decrease in overall deaths, particularly from respiratory illnesses and dementia, but an increase in deaths from diabetes. The study also found a reduction in the seasonality of deaths, indicating a possible impact of public health measures. The increase in diabetes deaths is unexplained and requires further investigation.