Public & Global Health: Health Beyond the Clinic

In August 1854, cholera hit Broad Street in Soho, London. The doctor John Snow marked the deaths on a map, saw them cluster around one water pump, and persuaded officials to remove its handle. He did not know about bacteria; he had a map, a hunch and a count. That is public health in one picture: no cure, no drug, a change made to a shared thing, and a drop in deaths among people who never knew they had been at risk.

A hundred and seventy years later the shared things are tobacco taxes, vaccination schedules, clean air, seat belts and how a country pays for its hospitals. This piece explains how public health works; it is not medical advice. For a health question, see a clinician; in an emergency, call your local emergency number.

Health is made outside the clinic

Ask what keeps a population healthy and doctors are, to the surprise of many, only part of the answer. Clean water and sewers, food, housing, work, education, income and the air all matter more for most diseases than treatment. A famous argument by the historian Thomas McKeown (1976) said that Britain's death rate fell in the nineteenth century mainly because people ate better, not because medicine improved. Later historians such as Simon Szreter credited public works and sanitation as well. The two sides disagree about the mix, not about the point: a society's health is mostly made upstream.

The same is true today. In the Whitehall studies, led by Michael Marmot from the late 1960s, British civil servants, all with secure jobs and access to the same health service, showed a gradient: each step down the grade ladder came with worse health. The WHO's Commission on Social Determinants of Health (2008) put the lesson in its title, Closing the Gap in a Generation. Social position, not only germs and genes, gets under the skin.

A second lesson comes from the epidemiologist Geoffrey Rose (1981, 1985): a population approach shifts everyone a little; a high-risk approach finds and treats the people at the top of the distribution. The high-risk approach is efficient for each person treated, but most cases come from the large middle group, because there are so many more people there. Rose called the result the prevention paradox: a measure that brings large benefits to the community offers little to each individual.

With the starting values there are about 858 cases a year among 100,000 people. The top 10% of scores produce only 41% of them, so 59% of cases occur in people nobody would call high-risk. Shifting everyone by 5 units prevents 29% of cases but needs about 398 person-years of effort per case prevented; treating only the top 10% prevents 12% but needs about 99. The narrow approach is four times as efficient and prevents less than half as much.

The transition from infection to chronic disease

As countries get richer, the diseases that kill them change. Abdel Omran named this the epidemiological transition in 1971: first an age of pestilence and famine, then of receding pandemics as sanitation and food improve, then of degenerative and man-made diseases such as heart disease, cancer and diabetes. Later writers added stages, and critics point out that it does not run in a straight line: many low- and middle-income countries carry a double burden of infections and chronic disease together, and some "chronic" diseases turn out to have infectious causes.

The latest World Health Organization data (for 2023) show it clearly. About 61 million people died that year; the top causes worldwide were ischaemic heart disease (9.5 million), stroke (6.8 million), chronic obstructive pulmonary disease (3.6 million), lower respiratory infections (2.7 million), Alzheimer's and other dementias (2.1 million), diabetes (2.0 million) and lung cancers (1.8 million).

Where	What the top ten causes of death look like, WHO 2023
Low-income countries	Seven of ten are communicable. Lower respiratory infections lead; diarrhoeal diseases are fifth; malaria, tuberculosis and HIV/AIDS appear.
High-income countries	Nine of ten are noncommunicable. Heart disease and stroke are in the top three; dementia is third and lung cancer fourth; lower respiratory infections (sixth) are the only infection.

Counting the burden: deaths, years and DALYs

Deaths alone mislead: a death at 30 costs more years than one at 90, and a disease that disables without killing does not appear. The disability-adjusted life year (DALY) counts one lost year of healthy life, whether lost by early death or by living with illness. It is the main unit of the Global Burden of Disease (GBD) study, run by the Institute for Health Metrics and Evaluation (IHME) in Seattle, and WHO publishes its own estimates; the two differ in methods and sometimes in numbers.

A disability weight runs from 0 (full health) to 1 (equivalent to death) and comes from surveys of how people rank states of health. The weights are debated: the GBD revised many between 2004 and 2010 (blindness fell from 0.594 to 0.195), dropped the early age-weighting that valued young adults' years more, and dropped discounting of future years. Critics say any such weighting hides value judgments; defenders say that without a common unit, we cannot compare a heart attack with a lifelong back problem.

The first preset gives 1,000 deaths × 30 years = 30,000 years of life lost, and no disability. The second has no deaths at all but 50,000 people living for 10 years at weight 0.2: 100,000 years lived with disability. By deaths alone the first looks worse; by DALYs the quiet, chronic one is more than three times as big. That is why lower back pain, depression and hearing loss rank high in burden tables even though they rarely kill.

Who pays: four ways to run a health system

Every health system answers the same question: who pays, and who provides? Four patterns recur, and most countries mix them.

• Beveridge model (named after William Beveridge's 1942 report): tax-funded, government-run. The UK's National Health Service, founded in 1948, is the classic example; Spain and the Nordic countries are close.
• Bismarck model: insurance funds paid by employers and workers, with private providers. It began with Germany's sickness insurance law of 1883; Germany, France and Japan work this way in different forms.
• National health insurance: one public insurer paying private providers. Canada's provinces and South Korea use it.
• Out-of-pocket: patients pay when they are sick. It is the main route where public systems are weak, and it pushes families into poverty.

Real systems vary: Switzerland requires everyone to buy regulated private insurance; the United States combines employer plans, public programmes (Medicare, Medicaid) and the uninsured; Brazil's tax-funded Sistema Único de Saúde was set up by the 1988 constitution; Thailand introduced a tax-funded universal coverage scheme in 2002; Rwanda built community insurance funds with donor money.

The United States spent 16.7% of its GDP on health in 2023, about $13,500 per person; Germany 11.7%, the UK 11.0%, Japan 10.7%. In Nigeria 72% of health spending was out of pocket, in India 44%, in Mexico 41%; in Thailand, which spends only 4.5% of GDP, it was about 10%. Spending, coverage and health are three different things.

Vaccines, herd immunity and eradication

The central number of infectious-disease dynamics is R₀, the average number of people one case infects in a fully susceptible population. If R₀ is above 1, an outbreak grows. Immunity shrinks the number: when a fraction v of people are immune, each case infects R₀(1 − v) others, and the outbreak dies when that falls below 1. The needed fraction is the herd immunity threshold.

The usual figures are 71 to 83% for smallpox, 80 to 86% for polio and 92 to 94% for measles (R₀ about 12 to 18). Real populations mix unevenly, so pockets of low coverage can keep a disease alive even when the national average looks high.

Set R₀ to 2.5 with no vaccination: the model gives a peak of about 24% of people infected at once and about 89% infected in total. Vaccinate 60% with a 95%-effective vaccine and 57% are immune, just under the 60% threshold: the effective R is 1.08 and only about 5% are ever infected. At 70% coverage, 66% are immune, the effective R is 0.84 and the outbreak barely starts. For measles the coverage needed is above 90%, which is why a few unvaccinated schools can bring it back.

Eradication is the extreme case: drive the number to zero everywhere. Smallpox is the only human disease so far. The WHO began an intensified programme in 1967, the last natural case was diagnosed in October 1977 (Ali Maow Maalin, in Somalia), and eradication was certified in May 1980; the last death was a laboratory accident in Birmingham in 1978. Stocks of the virus still exist at two WHO-approved laboratories, in the United States and Russia. Rinderpest, a cattle disease, was declared eradicated in 2011. Polio is near: the global programme began in 1988, wild poliovirus types 2 and 3 were declared eradicated in 2015 and 2019, and the African region was certified free of the wild virus in 2020. Type 1 persists in Pakistan and Afghanistan: 99 cases in 2024 (74 and 25), and about 38 reported by October 2025 (the full-year count is not verified here). The oral vaccine can also, rarely, seed outbreaks in under-vaccinated communities.

Tobacco: a long fight with a known cause

Smoking is the great proof that prevention works slowly. In 1950 Richard Doll and Austin Bradford Hill published a case-control study linking cigarettes to lung cancer, followed by their British doctors' cohort in 1954 (see Epidemiology & Evidence-Based Medicine, 35/58). The industry's response, documented in later litigation and in books such as Merchants of Doubt, was to manufacture doubt. Today WHO says tobacco kills more than 7 million people a year, of whom over 1.6 million are non-smokers exposed to smoke (2023 data).

The response was the first treaty negotiated under WHO: the Framework Convention on Tobacco Control, adopted in 2003 and in force since 2005, with 183 parties by WHO's count. It is backed by the "MPOWER" package (2007): monitor use, protect people from smoke, offer help to quit, warn about dangers, enforce bans on advertising, raise taxes. Raising tobacco taxes is widely regarded as one of the most effective measures. Australia introduced plain packaging in 2012; others followed. Newer products such as e-cigarettes divide experts: some health bodies see them as a route off cigarettes, others as a route on to nicotine for young people, and the evidence is still developing.

Pandemics and preparedness

An epidemic is more cases than expected in a place; a pandemic is one that spreads across continents; a disease is endemic when it circulates steadily. The 1918 influenza is the benchmark, with estimates of deaths spanning a wide range, commonly put near 50 million. HIV/AIDS is a pandemic that is still going; the 2014 to 2016 Ebola outbreak in West Africa caused more than 11,000 deaths; the 2009 H1N1 influenza spread worldwide.

COVID-19 showed how hard it is to count a pandemic. WHO estimated 14.9 million excess deaths (range 13.3 to 16.6 million) in 2020 and 2021, far more than officially recorded; an IHME-led study published in 2022 estimated more than 18 million. The difference comes from different methods and the fact that many countries record few deaths at home. Lessons the field drew included early surveillance, fast testing, supply stocks, trust and clear communication, and fair access to vaccines, which was unequal between rich and poor countries. The International Health Regulations (2005) require countries to report events; in May 2025 the World Health Assembly adopted a Pandemic Agreement, though as far as I could verify its annex on sharing pathogens and benefits was still being negotiated.

What a graduate just sees

• Most health is made upstream (water, food, housing, income); a clinic treats what upstream failed to prevent.
• A small shift across a whole population can prevent more cases than a large shift in the few at highest risk.
• Deaths undercount burden; years lost and years lived with disability change the ranking.
• As countries grow richer the leading causes of death move from infections to chronic disease, often leaving a double burden in between.
• Health systems differ in who pays and who provides; spending, coverage and outcomes are three different things.
• Herd immunity is 1 − 1/R₀, and it protects those who cannot be vaccinated only while coverage stays high everywhere.
• Every statistic about a pandemic depends on who counted and how; ask for the method.
• The best public-health measures are often boring: taxes, laws, pipes and schedules.

Where it shows up next

• Epidemiology & Evidence-Based Medicine (35/58) supplies the methods (cohorts, trials, bias) that public-health claims rest on.
• Public Policy (35/16) and Political Economy (35/17): who pays, and why reforms stall.
• Medical Ethics & Law (35/60): rationing, mandates and consent at population scale.
• Microbiology (35/50) and Immunology (35/57): the biology behind R₀, vaccines and resistance.
• In the world: ministries of health, WHO and national disease-control agencies, NGOs and foundations, health insurers, and every school-vaccination schedule.

If you want to go deeper

• 📘 Textbook. Michael Marmot, The Health Gap (2015) for the social-determinants view, and a standard introduction such as Bernard Turnock's Public Health: What It Is and How It Works (Jones & Bartlett), widely used in public-health schools.
• 📘 Textbook. Detels et al., Oxford Textbook of Global Public Health (Oxford University Press). The reference work for the global picture.
• 📘 Gentler. Hans Rosling, Factfulness (2018), and Steven Johnson, The Ghost Map (2006), the story of John Snow and the Broad Street pump.
• 🌐 Free course and data. OpenWHO hosts free WHO courses; Our World in Data's health pages and the IHME GBD Compare tool let you explore the numbers.