COVID-19 Mortality Working Group – Excess mortality continues in January 2023, but with less non-COVID excess mortality than in 2022

Catch up on the Actuaries Institute’s COVID-19 Mortality Working Group’s latest analysis of excess deaths.

Background

The COVID-19 Mortality Working Group has examined the latest Provisional Mortality Statistics, covering deaths occurring prior to 31 January 2023 and registered by 31 March 2023, released by the Australian Bureau of Statistics (ABS) on 28 April. This release also included the article COVID-19 Mortality in Australia, with details on all COVID-19 deaths occurring and registered by 31 March 2023.

We calculate excess deaths by comparing observed deaths to our “baseline” predicted number of deaths for doctor-certified deaths (by cause) and coroner-referred deaths (for all causes combined). 

Throughout this article, we separate COVID-19 deaths into:

• deaths “from COVID-19”, namely deaths where COVID-19 is listed as the primary/underlying cause of death;
• deaths that were “COVID-19 related”, namely deaths where the underlying cause of death has been determined as something other than COVID-19, but COVID-19 was a contributing factor mentioned on the death certificate (sometimes referred to as “with COVID-19”).

The COVID-19 deaths covered in this article are distinct from “incidental COVID-19” deaths, namely deaths where the person was COVID-19 positive at the time of death but COVID-19 was not recorded on the death certificate. These deaths are generally included in surveillance reporting where identified (other than where there is a clear alternative cause of death, such as trauma) but are not separately identified in the ABS statistics.

We have used additional data supplied by the ABS in a customised report in relation to COVID-19 deaths registered by 31 March 2023, namely the total number of deaths each week (doctor-certified and coroner-referred) both from COVID-19 and COVID-19 related.

Baseline Predictions

Our previous Actuaries Digital article discussed in some detail how we arrived at our baseline predicted deaths.  In short, our baselines by cause of death are set by extrapolating linear regression models fitted to Standardised Death Rates (SDRs), which are then re-expressed as numbers of deaths. That means that our baselines allow for changes in the size and age composition of the population, plus the continuation of pre-pandemic mortality trends.

As this is the first data released by the ABS in relation to 2023, we have estimated a baseline for 2023 by extrapolating our existing 2022 baseline models for another year.  Given the high level of excess mortality in 2022, and our intent for our baseline to reflect the expected number of deaths “in the absence of the pandemic”, we decided that it would be inappropriate to include any experience from 2022 in setting our baseline for 2023. 

Therefore, the baselines for our estimates of excess deaths are “in the absence of the pandemic” for each of the four years 2020 to 2023. We have not included any COVID-19 deaths in the baselines, as these would not exist in the absence of the pandemic.

As always, it is important to note that predicted death numbers are increasing faster from demographic changes (ageing and population size) than they are reducing due to mortality improvement, even though age-adjusted death rates are reducing.  Therefore, our model predicts higher baseline numbers of deaths in each successive year.

Excess deaths to 31 January 2023

Figure 1 shows the results of our analysis, comparing actual deaths each week to our predicted values and the 95% prediction interval.

Figure 1 – Weekly actual and predicted deaths – All Causes

The first three weeks of January 2023 were well above the upper end of the 95% prediction interval, as was the case for the majority of 2022. The last week of January 2023 was at the upper end of the prediction interval, well above the expected level.

Figure 2 shows deaths from COVID-19 and COVID-19 related deaths, noting that, given small numbers, weekly data for COVID-19 related deaths is not available for 2020 or 2021. 

Figure 2 – Weekly actual and predicted deaths – from COVID-19 and COVID-19 related*

Deaths from COVID-19 fell across the month of January, averaging 170 per week.  COVID-19 related deaths followed the same pattern as from COVID-19 deaths, also falling over the month of January.

Figure 3 – Weekly actual and predicted deaths – All Causes excluding deaths from COVID-19 and COVID-19 related deaths

Figure 3 compares actual and predicted deaths after removing deaths from COVID-19 and COVID-19 related deaths. It shows that non-COVID-19 deaths in the four weeks of January 2023 were within the 95% prediction interval. 

Excess deaths to 31 January 2023 by Cause of Death

Table 1 shows our estimate of excess deaths broken down by cause. 

As in our previous work, we have assumed that coroner-referred COVID-19 deaths will be 5% of all COVID-19 deaths in 2022, based on the experience of late 2021 and the emerging experience in 2022. If our estimate of coroner-referred COVID-19 deaths is too high (or low), this will not affect the total level of excess deaths measured; it will just mean that our estimate of non-COVID-19 coroner-referred deaths will be too low (or high) by the same amount.

Table 1 – Excess deaths in Australia – By Cause of Death for January 2023

In the month of January 2023:

• • total deaths were 8% (or +1,100) higher than predicted;
  • there were 760 deaths from COVID-19, representing two-thirds of the excess deaths;
  • while not shown in the table, 231 COVID-19 related deaths are included among the other causes of death, representing a further 20% of the excess deaths. The remaining 13% of excess deaths (c. 150) have no mention of COVID-19 on the death certificate, which is lower than the proportion for 2022 (33%); and
  • doctor-certified deaths from diabetes, dementia and other unspecified diseases were all significantly higher than predicted (by between 3% and 15%), while deaths from pneumonia were significantly lower than predicted (-21%).

Changes in data provided by ABS

With the data release for the new year, the ABS has made a small number of changes to the data supplied:

• • 1. Population estimates have been revised in accordance with the ABS’s usual estimation protocols. These revisions, which mainly affect the 2020 and 2021 years, have resulted in slightly lower population estimates and thus slightly higher SDRs. Our baselines for 2022 and 2023 are set using the SDRs for 2020 and 2021 for all causes of death other than respiratory disease and dementia. As these revisions to the population estimates are not yet reflected in our model, our 2022 and 2023 baseline estimates of deaths are probably slightly too low, meaning that our estimates of excess mortality are slightly overstated.
    2. Doctor-certified deaths from dementia have been expanded to include ICD codes G31.0 (Fronto-temporal dementia) and G31.8 (Lewy body dementia). We have compared the number of deaths included in the dementia category now with the data to 31 December 2022, and it shows that the ICD codes G31.0 and G31.8 increase the number of deaths in this category by around 3.5%. To allow for this, we have increased our dementia baseline by 3.5%, and deducted the same amount from our “other unspecified disease” baseline (where the ICD codes G31.0 and G31.8 were previously included).
    3. Doctor-certified deaths from “other cardiac conditions” (ICD-10 codes I26-I51) have been reported separately. These ICD codes are currently included in our “other unspecified disease” category. We have not yet separated other cardiac conditions from our “other” category as we need to set new baselines for both categories and have not yet done so.

The first two factors mean that there is a higher level of uncertainty in our measurement of excess mortality for the month of January 2023 compared to previous months. This will be resolved by next month, when we will have had the opportunity to re-set the baselines for all causes of death, including other cardiac conditions.

Further analysis

We have not estimated excess deaths by age group/gender or state/territory in this article, and we intend to only examine these breakdowns at the end of each quarter from now on. See our previous article for a detailed examination of these breakdowns to 31 December 2022.

Disclaimer

This monthly COVID-19 mortality analysis is intended for discussion purposes only and does not constitute consulting advice on which to base decisions. We are not medical professionals, public health specialists or epidemiologists.

To the extent permitted by law, all users of the monthly analysis hereby release and indemnify The Institute of Actuaries of Australia and associated parties from all present and future liabilities that may arise in connection with this monthly analysis, its publication or any communication, discussion or work relating to or derived from the contents of this monthly analysis.

COVID-19 Mortality Working Group

The members of the Working Group are:

• Angelo Andrew
• Karen Cutter
• Jennifer Lang
• Han Li
• Richard Lyon
• Zhan Wang
• Mengyi Xu

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