Measuring excess mortality in Victoria during the COVID-19 pandemic

Provisional deaths data for measuring changes in patterns of mortality during the COVID-19 pandemic and recovery period.

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Released
10/03/2021
Source
Provisional Mortality Statistics, Jan-Nov 2020

Introduction

Since the emergence of COVID-19, the number of deaths has been monitored closely in Australia and around the world in order to provide estimates of excess mortality that may potentially be related to the pandemic. Excess mortality is typically defined as the difference between the observed number of deaths in a specified time period and the expected numbers of deaths in that same time period. Measures of excess mortality can account for deaths due to COVID-19, any potentially misclassified or undiagnosed COVID-19 deaths and other mortality that may be indirectly related to the pandemic (e.g. relating to social isolation or changed access to health care). 

Over the period from January to November 2020, Australia recorded lower than expected mortality (see graph below) with decreases in the winter months being statistically significant. Lower than expected numbers of deaths were particularly notable for respiratory diseases including pneumonia. This is in contrast to many other countries where excess deaths have been recorded during the pandemic. 

Australia had two waves of COVID-19 infections during 2020. The first wave was recorded from mid-March to mid-April, with most states in Australia recording active infections and associated mortality. The second wave started in June, with the largest number of active infections and deaths occurring in Victoria. This report will focus specifically on Victorian deaths to examine the impact of COVID-19 and especially the second wave of infections, on all-cause and cause-specific patterns of mortality. 

  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.

Measuring excess mortality

Across the world, health and statistical authorities have sought to measure excess mortality during the COVID-19 pandemic. There are many different methodologies that are designed for this purpose, with the suitability of particular methods often dependent on factors such as data quality and collection methods, or outcomes sought from analysis. 

The ABS has adopted aspects of a methodology used by New South Wales (NSW) Health, applying a cyclical linear regression with a robust estimation procedure to produce an expected number of deaths for 2020 for all cause and cause-specific mortality to identify significant changes in patterns of mortality over time. See the methodology section at the end of this article for detailed information about the model applied.

Interpreting results

Each section below presents two graphs – The first graph is a time series of doctor certified deaths from January 2015 to November 2020 that has the number of actual observations plotted against the expected number of deaths estimated from the regression. The upper and lower thresholds (1.96 standard errors) of the regression are also plotted. The second graph focusses only on 2020, allowing closer inspection of patterns of death during the COVID-19 pandemic. 

At any point in time, if no temporary health hazards influence the number of deaths (i.e. community transmission of influenza or COVID-19) then there is a 95% chance that the expected number of deaths would lie between the upper and lower bounds of the confidence intervals. When actual observations (counts of death) exceed the upper threshold or drop below the lower threshold this indicates a statistically significant change in the pattern of mortality. 

Different approaches can be used to calculate the number of excess deaths. Counts of excess can be taken as the difference between the average expected number of deaths and the actual observed number. This approach risks over-estimating the number of excess deaths as the expected count lies between the upper and lower bound. Counts of excess can also be taken as the difference between the upper threshold of the expected number of death and the actual observed number. This approach results in a lower number of excess deaths, but focusses more clearly on statistically significant changes in mortality. 

Identifying significant changes in the pattern of mortality during the COVID-19 pandemic compared to previous years is the aim of this report. Counts of deaths that are above the upper bound of the confidence interval (threshold) are considered to be “excess” and will be referred to as such in this report. Counts of excess deaths described in this report refer only to the number above the upper threshold.

A single week above threshold does not necessarily suggest excess mortality. Prolonged periods (2 or more weeks) where counts exceed thresholds suggest more strongly that the numbers of deaths are above or below normal. This should be considered when analysing the data in this report. 

All-cause mortality in Victoria (doctor certified deaths)

  • Excess mortality for all doctor certified deaths in Victoria was observed during the first wave of COVID-19 in the weeks starting 23 and 30 March 2020. Observed numbers of deaths exceeded the upper threshold of expected numbers by 28 during that period. 
  • Those weeks in March coincided with high rates of COVID-19 infections and the implementation of stricter lock-down measures across Australia.
  • Excess mortality for all doctor certified deaths was observed during the second wave of COVID-19 in the four weeks between 27 July and 17 August 2020. Observed numbers of deaths exceeded the upper threshold of expected numbers by 125 during that period. 
  • The graph tracking mortality through 2020 shows counts both with COVID-19 deaths included and without. This provides insight into both direct COVID-19 mortality as well as patterns of mortality from causes other than COVID-19. 
  • During wave 2, excess mortality recorded in Victoria was largely due to deaths from COVID-19. Observed numbers of deaths from causes other than COVID-19 track more closely to expected numbers for the 4 weeks beginning 27 July. 
  • Between 6 April and 3 May the observed number of deaths was largely above expected numbers. However, numbers of deaths did not exceed upper thresholds during that period so no excess mortality was recorded. 
  • Numbers of death in Victoria were below lower thresholds for the weeks beginning 6 July and 13 July, with 25 deaths less than lower threshold counts recorded in those two weeks. Analysis of deaths for all of Australia highlighted significantly lower than expected counts from 1 June to mid-July. 
  • There were 21 COVID-19 deaths in Victoria that were certified by a doctor during the first wave of the pandemic and 730 during the second wave. Coroner referred deaths are excluded from this analysis. 
  • The last time excess mortality was observed in Victoria was in 2017 when a severe influenza season led to 103 excess deaths between July and September of that year.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.

All-cause mortality by region (Greater Melbourne vs Rest of Victoria)

  • There were 165 excess deaths in the Greater Melbourne region during the second wave of the pandemic. Deaths that exceeded the upper threshold of expectation occurred between the weeks beginning 27 July and 17 August. 
  • Excess deaths during the second wave in Greater Melbourne were largely due to COVID-19. 
  • During the first wave there were two weeks (23 and 30 March) in Greater Melbourne where deaths exceeded the upper threshold, accounting for 6 excess deaths. 
  • From September, numbers of deaths have remained in the expected range for Greater Melbourne. 
  • In the week beginning 18 May the rest of Victoria recorded 22 deaths above the upper threshold of expectation. While this is a single time point it follows a number of weeks where deaths are above expected projections, though not reaching statistical significance. 
  • During the second wave of the pandemic, the rest of Victoria experienced no excess mortality. Numbers of deaths were generally within the expected range except for the week beginning August 31 where deaths fell below lower the threshold. 
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  5. There are 1898 deaths excluded from the all counts for greater Melbourne and rest of Victoria due to being an interstate or not stated death. 
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  5. There are 225 deaths excluded from the all counts for greater Melbourne and rest of Victoria due to being an interstate or not stated death. 
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  5. There are 1898 deaths excluded from the all counts for greater Melbourne and rest of Victoria due to being an interstate or not stated death.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  5. There are 225 deaths excluded from the all counts for greater Melbourne and rest of Victoria due to being an interstate or not stated death.

Cause-specific mortality

While all cause mortality provides a more accurate picture of patterns of mortality during the pandemic it is important to look at cause-specific mortality to provide insights into how individual causes have changed. Specific causes may experience significant changes which can be masked at the all-cause level. The following section focusses on excess mortality analysis for selected causes of death certified by a doctor in Victoria in 2020. Deaths are analysed by underlying cause of death only. 

Ischaemic heart disease (I20-I25)

  • Numbers of deaths in Victoria from ischaemic heart disease were generally within the expected range throughout 2020. 
  • Numbers of deaths exceeded upper thresholds by small amounts in the weeks beginning 6 April, 28 September and 9 November (4, 2 and 1 death respectively). These were only single observations and are therefore not considered to be statistically significant. 
  • Ischaemic heart disease is the leading cause of death in Australia. Deaths due to ischaemic heart disease have been declining over time. This has resulted in the regression producing a reduced number of expected deaths each year.
  • Excess mortality was recorded for ischaemic heart disease in July and September of 2017. This aligns with a severe influenza season and excess mortality recorded among other causes at that time. 
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.

Cerebrovascular diseases (I60-I69)

  • Deaths due to cerebrovascular diseases (CVD) exceeded the upper threshold in the weeks beginning 3 and 10 August, accounting for a total of 15 excess deaths. 
  • In the weeks beginning 18 May and 9 November 2020 the number of deaths due to CVD exceeded the upper threshold by 9 and 4 deaths respectively. Both of these weeks are both single points in time and as such caution is advised when interpreting these results. 
  • Deaths have remained in expected ranges for CVD in all other weeks for 2020. 
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.

Respiratory diseases (J00-J99)

  • Deaths due to Respiratory diseases (including diseases such as influenza, pneumonia and chronic lower respiratory diseases) exceeded the upper threshold in weeks beginning 23 and 30 March accounting for 10 excess deaths.
  • From the week beginning 8 June until the week beginning 9 November there were significantly lower than expected numbers of deaths due to respiratory diseases in Victoria (excluding the week beginning 2 November). A total of 199 deaths less than lower thresholds were recorded during that period. 
  • In 2017 there were 128 excess deaths due to respiratory diseases. The majority of those excess deaths were due to the severe influenza season.
  • Deaths due to COVID-19 are not included in the analysis for respiratory diseases. For a weekly count of deaths due to COVID-19 that were certified by a doctor see Table 1.1 in the weekly dashboard in data downloads. 
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.

Chronic lower respiratory conditions (J40-J47)

  • Deaths due to Chronic lower respiratory diseases (e.g. emphysema and asthma) exceeded the upper threshold in weeks beginning 23 and 30 March accounting for 5 excess deaths. 
  • Numbers of deaths from Chronic lower respiratory conditions have been below expected counts since 25 May, with counts below lower thresholds observed for several weeks through July, August and September.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.

Influenza and pneumonia (J09-J18)

  • Numbers of deaths due to influenza and pneumonia were above expected counts from the week beginning 16 March 2020 to the week beginning 13 April. 
  • The week beginning 13 April was the only week where the number of deaths exceeded the upper threshold. This is a single point in time and should be interpreted with caution. 
  • In Victoria in 2020 there were 7 deaths due to influenza. 
  • Public health measures put in place to prevent the spread of COVID-19 infections can also be effective in limiting the spread of other infectious agents including influenza. 
  • The influenza season resulted in excess mortality in 2015, 2016, 2017 and 2019. 
  • In 2017 there were 124 excess deaths due to influenza and pneumonia with excess deaths recorded between July and October.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.

Pneumonia (J12-J18)

  • Pneumonia is commonly caused by seasonal viruses including influenza. Pneumonia is the most commonly certified consequence of COVID-19 leading to death. 
  • To remove the confounding effect of influenza on projected number of expected deaths pneumonia has been analysed separately with results detailed in the two graphs below. 
  • There were 14 excess deaths due to pneumonia during wave 1 of the COVID-19 pandemic in Victoria. 
  • From 1 June the number of deaths due to pneumonia has been lower than expected numbers, with numbers falling below lower thresholds for several weeks between August and November.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.

Cancer (C00-C97, D45, D46, D47.1, D47.3-D47.5)

  • In the weeks beginning 4 May and 9 November 2020 the number of deaths due to cancer exceeded the upper threshold by 13 and 9 deaths respectively. Both of these weeks are single points in time and as such caution is advised when interpreting these results. 
  • For the two week period from 13 July 2020 numbers of cancer deaths dropped below the lower threshold. 
  • Between 2015-2019 cancer mortality has generally fallen between expected ranges. Intermittent points where the number of deaths have exceeded the upper threshold or dropped below the lower threshold of expectation have not been prolonged. This same pattern of death is seen for cancer mortality in 2020. 
  • This analysis has covered all cancers grouped together. Results may differ for specific cancer types. 
     
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.
  1. This graph is compiled by the date the death occurred.
  2. This data is considered to be provisional and subject to change as additional data is received.
  3. Weeks in this graph always start on a Monday, with each year following on from the previous one (eg week 52 has 28 December 2015 to 3 January 2016). In the main publication, week 1 is always 1-7 January. 
  4. Refer to explanatory notes in the Methodology section for this article for more information regarding the data in this graph.

Diabetes (E10-E14)

  • During the first wave of the COVID-19 pandemic, deaths due to diabetes were above expected projections from the week beginning 23 March to 4 May. For two of these weeks (30 March and 13 April) diabetes mortality exceeded upper thresholds. 
  • In the week beginning 10 August 2020 the number of diabetes deaths slightly exceeded the upper threshold (2 excess deaths). This is a single point in time and should be interpreted with caution. 
  • People with diabetes can be susceptible to infections due to a compromised immune system. Mortality can be influenced by infectious disease activity in the community.