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

Abstract

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 0.96 (0.95-0.98)] with reductions across states, ages and sex strata. There were fewer deaths from respiratory illness [RR 0.79 (0.76-0.83)] and dementia [RR 0.95 (0.93-0.98)] but more from diabetes [RR 1.08 (1.04-1.13)]. Seasonal variation was reduced for deaths overall [AR 0.94 (0.92-0.95)], and for deaths due to respiratory illnesses [AR 0.78 (0.74-0.83)], 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.