The Epidemiological Transition and Health Trends

The epidemiological transition is the long-term shift in the main causes of death in a population, from infectious diseases, malnutrition and complications of childbirth to chronic, non-communicable diseases such as heart disease, cancer and diabetes, as life expectancy rises and societies develop. In brief: Abdel Omran proposed the model in 1971, with three stages: the age of pestilence and famine, the age of receding pandemics and the age of degenerative and man-made diseases. Today, non-communicable diseases cause roughly three quarters of all deaths worldwide, but many low-income countries face a “double burden” of infectious and chronic disease.

The transition links changes in health to changes in the age structure and is a key part of understanding population change. This guide explains the stages of the model, the reasons for the shift, current global health trends and exceptions, compares the stages in a table, works through examples, outlines the history and corrects common mistakes.

What are the stages of the epidemiological transition?

Stage 1: The age of pestilence and famine

Mortality is high and fluctuates because of epidemics, famines and wars. Infectious diseases such as plague, smallpox and cholera, and deaths among children and mothers, dominate. Life expectancy is low, about 20 to 40 years. This was the situation in most of the world until the 18th century, and it still applies to some very poor or conflict-affected regions.

Stage 2: The age of receding pandemics

Mortality falls as epidemics become less frequent and less deadly because of better nutrition, clean water, sanitation, hygiene and, later, vaccination and antibiotics. Life expectancy rises to 30 to 50 years or more. Population growth accelerates because deaths decline faster than births. This stage occurred in Europe during the 19th century and in many developing countries in the 20th century.

Stage 3: The age of degenerative and man-made diseases

Infectious diseases are controlled, and most people die from chronic and degenerative diseases, such as cardiovascular disease, cancers, diabetes and respiratory disease, which are related to aging and lifestyle (smoking, diet, physical inactivity), as well as accidents and pollution. Life expectancy exceeds 50 and goes beyond 70. Mortality is low and fairly stable, and fertility is also low.

Later stages

Olshansky and Ault (1986) added a fourth stage, the age of delayed degenerative diseases, in which medical advances and healthier living postpone deaths from chronic disease to older ages, so most deaths occur after 70 or 80. Others have described a fifth phase of re-emerging infections and antibiotic resistance, which includes HIV/AIDS, new influenza strains and Covid-19.

What drives the transition?

The main driver of early declines in mortality was improved living standards: food supply, housing, clean water and sanitation, along with public health measures. Medical technology (vaccines, antibiotics, safe childbirth) became important in the 20th century. Education, particularly of mothers, and income growth also matter. Later, deaths from chronic disease fall because of better prevention and treatment of heart disease, reductions in smoking and improved care. The shift in causes of death is also partly a result of changing age structure: as more people survive to older ages, a larger share of the population is at risk of cardiovascular disease and cancer.

What are the current health trends?

• Non-communicable diseases (NCDs): according to the World Health Organization, NCDs, led by heart disease and stroke, cancers, chronic respiratory disease and diabetes, account for about 74% of all deaths, and most of the premature NCD deaths occur in low- and middle-income countries.
• Double burden: many low- and middle-income countries have infectious diseases (malaria, tuberculosis, HIV, respiratory infections), undernutrition and rising NCDs at the same time, which strains health systems.
• Rising life expectancy: global life expectancy increased from about 47 years in 1950 to about 73 years in 2019. It fell by about 1.5 to 2 years during the Covid-19 pandemic in 2020–2021, and has since largely recovered. The gap between countries is large: more than 80 years in Japan and Switzerland and in the low 50s or 60s in several countries of Sub-Saharan Africa.
• Risk factors: tobacco, unhealthy diets, obesity, alcohol, air pollution and inactivity drive NCDs. Obesity is now rising in many low-income countries.
• Mental health and aging: depression, dementia and conditions of older age are growing as populations age.
• Infectious threats: antimicrobial resistance, new and re-emerging diseases and the effects of climate change on vector-borne diseases.

The stages compared

Worked example: causes of death and life expectancy

The values are hypothetical and illustrate typical calculations.

1. Shares of deaths: a country records 200,000 deaths in a year: 130,000 from non-communicable diseases, 50,000 from infectious and maternal causes and 20,000 from injuries. The shares are 130 ÷ 200 = 65%, 50 ÷ 200 = 25% and 20 ÷ 200 = 10%. With 65% from NCDs, it is in the third stage, but the 25% share from infections suggests a double burden.
2. Mortality rate: the country has 8 million people. The crude death rate is 200,000 ÷ 8,000,000 × 1,000 = 25 per 1,000. The rate from NCDs alone is 130,000 ÷ 8,000,000 × 1,000 = 16.25 per 1,000.
3. Change over time: thirty years ago, infectious diseases caused 55% of the deaths. Now they cause 25%, a drop of 30 percentage points, or 30 ÷ 55 = 55% in their relative share.
4. Gain in life expectancy: a rise from 52 years to 68 years in 40 years is 16 years, an average of 16 ÷ 40 = 0.4 years of life expectancy gained per year.
5. Age structure effect: a population in which 8% are aged 65 and over has an NCD death rate of 4 per 1,000. If the share of people over 65 doubles to 16% and age-specific rates stay the same, NCD deaths rise sharply even without any increase in risk at a given age.
6. Premature deaths: if 30% of NCD deaths (130,000 × 0.30 = 39,000) occur before age 70, these are premature deaths that are largely preventable.

How did the theory develop?

The Egyptian-American demographer Abdel Omran published his theory of the epidemiological transition in 1971, based on the experience of Western Europe and other regions. Thomas McKeown had argued in the 1960s and 1970s that improved nutrition, rather than medicine, explained most of the fall in mortality in England and Wales since the 18th century, a view that later scholars have qualified by pointing to the role of public health measures such as sanitation. Olshansky and Ault proposed the fourth stage in 1986, and the HIV/AIDS epidemic and the emergence of other infections in the late 20th century led to discussions of reversals. Covid-19 in 2020 showed that pandemics can still cause major excess mortality, especially among the old and those with chronic disease. International targets, such as SDG 3 on health and well-being, aim to reduce both infectious and NCD burdens.

Which mistakes are common?

Mistake 1: Treating the stages as a strict one-way path

Countries can move backward during crises, such as war or the HIV epidemic, and many experience a mix of stages at the same time.

Mistake 2: Assuming that chronic disease is only a problem of rich countries

Most NCD deaths occur in low- and middle-income countries, where health systems are often less able to cope.

Mistake 3: Crediting medicine alone for falling mortality

Nutrition, clean water, sanitation, housing and education made major contributions, in addition to vaccines and treatments.

Mistake 4: Reading rising NCD deaths as worsening health

Part of the increase is due to more people surviving to older ages, where chronic disease is more common.