Weekly all-cause mortality surveillance (week 35 report, up to week 31 2024 data)
Updated 19 December 2024
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Overview
This report includes details of the weeks in which all-cause observed deaths were higher than an expected threshold. This is calculated using a European-wide algorithm called EuroMOMO. It can be used to identify weeks when factors such as infectious disease activity or extreme temperature may have caused higher mortality rates than expected and require further investigation.
This report covers the UK. Analysis is stratified by age and region in England, and by all deaths combined in Northern Ireland, Scotland and Wales.
Main points
In week 31 of 2024, no signal of high mortality above the baseline was seen in England using all ages combined or for those aged under 5 years, aged 5 to 14 years, aged 15 to 64 years, and aged 65 years and over, or in any region. No signal of high mortality above the baseline was seen in Scotland or Wales using all ages combined. Data was not available for Northern Ireland for week 31.
Identifying signals of high all-cause mortality in subpopulations, UK
This analysis uses all-cause deaths by week of death occurrence with a correction for delays from death to registration using the standardised EuroMOMO algorithm. The algorithm used also produces a baseline estimate and z-score thresholds, with results above 2 z-scores regarded as a signal.
Figure 1 shows the output for England using all ages combined and includes indication of the main circulating influenza subtypes and recent SARS-CoV-2 periods which align with high mortality signals. Last season was a mixed A/H1N1pdm09 and A/H3N2 season.
In England, aggregated death registrations are provided to UK Health Security Agency (UKHSA) by the General Register Office (GRO). Mortality by week of death occurrence above the 2 z-score threshold was not seen overall in week 31 of 2024, nor in any age group or region. The weeks where a signal was identified (since week 40 of 2023) are shown in tables 1 and 2.
In the devolved administrations, data is based on GRO data for Wales, National Records of Scotland (NRS) data for Scotland, and Northern Ireland Statistics and Research Agency (NISRA) data for Northern Ireland. No signal of high all-cause mortality above the baseline for all ages was observed in Scotland or Wales in week 31 applied by week of death occurrence (Table 2). Data was not available for Northern Ireland for week 31.
Note that the data is provisional because of the time delay in registration, so numbers may vary from week to week. Data presented in this week’s report supersedes data presented in reports from previous weeks.
Figure 1. Weekly observed and expected number of all-cause deaths in all ages, with the dominant circulating respiratory virus, England, 2017 to week 31 of 2024
Note: the recent weeks’ data are estimates which may be subject to registration delay corrections and therefore should be interpreted with caution. These estimates may differ in future reports as more deaths are registered.
Table 1. Weeks with a high mortality signal by age group, England [note 1]
| Age group (years) | Signal in week 31 2024? | Weeks with a signal since week 40 2023 |
|---|---|---|
| Under 5 | No | Weeks 41, 49, 50, 5, 6 |
| 5 to 14 | No | Weeks 4, 16, 21 |
| 15 to 64 | No | Weeks 49, 1 |
| 65 and over | No | None |
[note 1]: Signal is defined as being above the 2 z-score threshold by the EuroMOMO algorithm.
Table 2. Weeks with a high mortality signal by UK country, for all ages [note 1]
| Country | Signal in week 31 2024? | Weeks with a signal since week 40 2023 |
|---|---|---|
| England | No | None |
| Wales | No | None |
| Northern Ireland | Not assessed | None |
| Scotland | No | Weeks 51, 52, 1, 3, 4 |
[note 1]: Signal is defined as being above the 2 z-score threshold by the EuroMOMO algorithm.
Glossary
Z-score
A z-score is a statistical measure of how many standard deviations above the baseline threshold the number of deaths was. For example, a z-score of 2 means that the number of deaths was 2 standard deviations above the baseline threshold. Chance signals using a 2 z-score threshold are expected about 2.5% of the time.
Data sources and methodology
Seasonal variation in mortality is seen each year, with a higher number of deaths in winter months compared with the summer. Additionally, peaks of mortality above this expected higher level typically occur in winter, most commonly the result of factors such as cold snaps and increased circulation of respiratory viruses, in particular influenza. In summer, peaks can arise because of heatwaves.
The baseline shown in Figure 1 comes from the standardised EuroMOMO algorithm which aims to give expected mortality in the absence of an acute event that may increase mortality. Such events include when influenza circulation is high, or extreme temperatures. The algorithm uses 5 baseline years and incorporates a trend and seasonality. Note that the COVID-19 pandemic period from March 2020 to March 2022 is excluded from the baseline calculation.
This weekly mortality surveillance aims to provide timely detection and reporting of signals that mortality is above baseline seasonal levels. These signals support public health risk assessment, which may include investigation of possible causes.
High mortality is defined as a statistically significant (above the upper 2 z-score threshold) number of deaths reported over the expected number of deaths for a given point in the year. This definition allows for weekly variation in the number of deaths.
The aim is not to assess general mortality trends or estimate the deaths attributable to different factors. Attribution of above-baseline mortality is done using more detailed analyses, incorporating information on possible causes such as temperature and influenza rates (for example, annual influenza surveillance and heat mortality monitoring reports).
Background information
Other assessments of all-cause mortality
A graphical z-score-only version of the EuroMOMO output is available for England, Scotland, Wales, Northern Ireland and across Europe from the EuroMOMO hub using data provided to the hub by each country. The hub produces a Europe-wide aggregated output and results from 28 countries for comparison of signals across Europe using a standard method.
The provisional number of weekly deaths registered in England and Wales is published online by the Office for National Statistics (ONS). Estimates of excess mortality are also published by the ONS using a method that compares deaths by week of registration to a baseline calculated using multi-year trends in the mortality rate, stratified by week, age, region and sex.
The Office for Health Improvement and Disparities (OHID) also produces the Excess mortality within England report, which provides estimates of expected deaths by month of registration for population subgroups and by cause of death.
The different methods used in the UK for mortality assessment, and their varied purposes, are discussed in more detail in Measuring excess mortality: a guide to the main reports.
Feedback and further information
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