In the UK and other countries, there has been concern about excess mortality compared to previous years, continuing beyond the peak waves of mortality associated with the pandemic¹. Some of these are attributable to Covid-19, which is still an important case of death, but there has also been a higher-than-expected number of non-covid deaths^{2 3}.

Given the characteristics of people most vulnerable to dying directly from Covid-19, the pandemic is likely to have brought forward deaths in some people who would otherwise have died within a few years⁴, although the Years of Life Lost (YLL) directly from Covid-19 in Scotland early in the pandemic were still substantial⁵. This displacement effect would be expected to lead to mortality subsequently being lower than previous years, rather than the continuing higher rates that are observed.

There is debate about the appropriate baseline to define ‘excess’ mortality⁶. One common method has been to compare with the average mortality rate for the same week or month in the previous 5 years. It is not appropriate to include 2020 in the baseline as mortality was inflated by the first waves of Covid-19, but an alternative baseline can be used that excludes 2020⁷. As the population is ageing, changes in age structure in the past 5-6 years mean that comparisons of crude mortality counts or rates are likely to be misleading¹. Age-standardised mortality rates provide a better comparison⁸ and, since 2021, have also shown an excess over pre-2020 rates. However, comparisons even of age standardised rates may be misleading when the population age structure has changed. Life expectancy is an alternative measure to show changes in mortality after accounting for changes in the population age structure.

There are several possible explanations for the continuing high mortality. These include: the longer term impacts of Covid-19 disease⁹; the effects of delayed or missed healthcare due to continuing health service pressures^{1 10}, including ‘secondary prevention’ measures¹¹; high rates of influenza and other respiratory infections that occurred following lifting of physical distancing measures; the wider impacts of the pandemic response operating through a range of economic and social pathways¹⁰, the impacts of wider political and societal pressures including the cost-of-living crisis¹², the summer 2022 heatwave¹³, and continuation of the previously noted stalling or reversal of improvements in mortality that were of concern long before the pandemic¹⁴.

In the UK, death rates in more deprived populations were already increasing before the pandemic, and at the national level long-term improvements in mortality had stalled from around 2012^{15 16}. This affected both men and women, almost all age groups and has been observed for many different causes of deaths. Similar trends have been seen, to different degrees, in other countries. A large body of research studying the reasons for these pre-pandemic trends concluded that these trends were associated with austerity policies introduced in the UK and other countries from the early 2010s ^{14 17 18}. Many of the financial and social impacts of austerity have been exacerbated by the pandemic and the more recent cost of living crisis¹⁹.

A critical understanding of the reasons for continuing high mortality rates is important to inform policy responses. Before conducting analytical work to investigate the reasons, it is important to identify all the hypotheses put forward to explain the trends, and any analyses already completed to investigate these. A scoping review is an appropriate way to collate and map the literature on a topic. We carried out a preliminary search of MEDLINE, the Cochrane Database of Systematic Reviews and JBI Evidence Synthesis on 23^rd May 2023 and identified no current or underway systematic reviews or scoping reviews on the topic of mortality trends since 2021.

We therefore propose a scoping review that will aim to assess the extent of current literature theorising or explaining the continuing higher-than-expected mortality beyond the peak of Covid-19 deaths. The review will focus on high income countries and will seek to identify all the hypotheses that have been suggested for these trends, and to identify and critically appraise any analytical studies investigating these hypotheses.