Covid-19 has been the world's largest health setback in more than 70 years as measured by life expectancy, according to the Global Burden of Disease (GBD) 2021 study, with researchers saying the long-term impacts of the pandemic may probably not be known for several years.
The latest iteration of the GBD, published in a series of six articles in The Lancet, reveals that because of inadequate data systems and huge lags in alternative measurement methods for age-specific and cause-specific mortality, controversy still surrounds the true impact of Covid-19 in sub-Saharan Africa.
In South Africa, for instance, the Civil Registration and Vital Statistics system showed large increases in mortality rates in older age groups during the pandemic; Health and Demographic Surveillance Sites in the country have largely not reported on the effects of the pandemic, even as of January 2024.
Yet in countries with complete or nearly complete civil registration and vital statistics data, the collaborators said we now have a detailed understanding of the effects of the first two years of the pandemic.
Preliminary all-cause mortality reporting from countries like Canada, Finland, Japan and Australia suggests larger than expected increases in mortality in 2022 and 2023, although, they stress, wide heterogeneity of the number of cases and deaths and long lags in reporting mean the full impact of the pandemic might not be known for several years.
And despite data limitations, we now have good understanding of the long-term trends at least in age-specific mortality for the world.
Risk factors
For the past three decades, the GBD has provided a comprehensive assessment of global health, examining demographic trends from 1950 onwards, causes of death from 1980 onwards, and the full health impacts of diseases and risk factors from 1990 onwards at the country level and at the sub-national level for 21 countries.
For GBD 2021, said study collaborator Professor Christopher Murray from the University of Washington, 328 938 sources were used, enabling the calculation of more than 607m estimates – although many data gaps remain in low-resource settings.
While the impact of the pandemic is a central theme in the most recent findings, forecasts highlight that future trends might be influenced by factors like the obesity epidemic, increased substance-use disorders, and climate change, while the study also underlines opportunities to alter the trajectory of health for the next generation.
Over the past 70 years, the world has had remarkably sustained progress in lowering mortality for both children and adults.
Life expectancy increased by 22.7 years (95% UI 20.8–24.8) between 1950 and 2021.
There have been major global setbacks, like the increase in adult mortality in former Soviet Union territories in eastern Europe and central Asia in the 1990s, the sharp increase in adult mortality in countries most affected by the HIV epidemic before the roll-out of ARV therapy, and the more focal impact of conflict and natural disasters, like the genocide in Rwanda in 1994, the tsunami in the Indian Ocean in 2004, and the Haitian earthquake in 2010.
Between 1950 and 2021, we witnessed major decreases in deaths from infectious disease, particularly among children, driven by improvements in sanitation, the delivery of specific interventions (e.g, childhood vaccinations), and increased access to effective healthcare.
From 1950 – the first year for which GBD estimates life expectancy – until the beginning of the pandemic, longevity for global populations generally improved, with increasing educational attainment, increasing income per person, and remarkable technical innovation in health-enhancing products and methods of delivery.
The reversal of the trends in life expectancy from the pandemic has been remarkable, given the nearly continuous pace of progress at the global scale otherwise seen over nearly seven decades.
But even before then, warning signs of new challenges emerged in high-income countries: the steady decrease in cardiovascular disease mortality had stopped or even reversed in several countries.
This observation is probably driven by the increase of obesity and the associated increase in fasting plasma glucose. More general slowdowns in the progress made in reducing mortality have also been driven in some countries by an increase in opioid deaths, particularly from fentanyl overdoses.
Long-term trends in these behaviours risk limiting future progress, or at least slowing progress, compared with what might have been. Furthermore, other global threats, like antimicrobial resistance, bioterrorism fuelled by malicious use of artificial intelligence, and climate change and its myriad effects, including increasing food insecurity in heat-stressed environments, continue to threaten to derail the general trends of progress.
Fertility rates
In GBD 2021, considerable attention was devoted to trends in age-specific and total fertility from 1950 to 2021, and forecasted to 2100.
The world has had an incredible fertility transition, most countries having total fertility rates below the replacement level of 2.1 children per woman.
Driven by increases in women’s education, needs met with modern contraceptive methods, urbanisation, and lower child mortality, fertility rates can drop rapidly.
Our analyses suggest that as women become more educated and reproductive health services become more widely available, the completed cohort fertility rate (i.e, the average number of children born during childbearing years to females from a specified birth cohort) is projected to decrease to 1.4 or less.
There are concerns some governments will attempt to pressure women to stay at home and have more children or even restrict their reproductive rights as a mechanism to increase birth rates, as was done in Romania in the 1960s to 1980s, at great cost to maternal and child health, labour markets, and educational outcomes.
The global community must be vigilant and advocate wherever necessary to solve declining population numbers through other strategies.
By contrast, slow decreases or the beginning of decreases in estimated total fertility rates in western sub-Saharan Africa – from 6.94 (95% UI 6.62–7.25) in 1950, to 4.29 (4.03–4.58) in 2021, and 2.72 (2.32–3.15) in 2050 – mean the total population for the whole of sub-Saharan Africa will probably continue to grow, potentially until the end of the century.
Death and disability
The articles in our series on causes of death, disability-adjusted life-years (DALYs) and risk factors highlight the complex pattern of disease burden globally, beyond the Covid-19 shock.
We also observed many secondary transformations. First, high BMI and high fasting plasma glucose continue to rise, and the associated prevalence of diabetes is increasing.
Notably, the trajectory for diabetes mortality seems to be more complex, with diabetes deaths decreasing in some countries that have increasing prevalence. Other risks that need urgent attention because their burden is worsening, or their burden is large and not improving, include high systolic blood pressure, sugar-sweetened beverage consumption, low physical activity, and drug use.
Second, ambient particulate matter air pollution remains a major cause of attributable DALYs and is rising globally, particularly in south Asia.
Third, depressive disorders and anxiety disorders have increased.
Fourth, child mortality steadily declined from 1990 to 2021, including during the pandemic – in sharp contrast to early predictions during the pandemic that child mortality would surge.
This disconnect between early modelling studies and the empirical findings is a reminder that purely hypothetical modelling studies must be interpreted with caution.
Finally, the spatial pattern of self-harm and interpersonal violence is highly heterogeneous across locations, with some countries and territories having three orders of magnitude higher rates than others.
GBD 2021 includes comprehensive forecasts of the burden of disease through to 2050.
The reference scenario, a probabilistic forecast of what is most likely to occur, incorporates all the GBD risk factors. Care has also been taken to include the most direct effects of climate change by incorporating increased daily temperature (and decreases in cold-related deaths) into the model.
The Lancet Commission on 21st-Century Global Threats to Health is working to quantify, or at least characterise, some major potential threats, including climate change, through a multiplicity of pathways, like food insecurity, pandemics, antimicrobial resistance, nuclear escalation of conflicts, malicious use of artificial intelligence, and the increase in diabetes, obesity, addiction and ageing.
According to GBD 2021, three key risk factors need to be addressed to have a major impact: tobacco consumption, high BMI and high blood pressure.
As national health system leaders consider the potential to reduce NCD risks in their countries, strategies to address these major risk factors (and other NCD risks) should feature prominently in national debates.
Prof Christopher Murray, DPhil, Institute for Health Metrics and Evaluation, University of Washington, USA.
The Lancet article – Findings from the Global Burden of Disease Study 2021 (Restricted access)
See more from MedicalBrief archives:
Poor diet a factor in 20% of deaths — Global Burden of Disease study
SA's great misalignment between development and health – Global Burden of Disease study
Plunging global fertility rates will lead to big world divide