Stopping Illness Before, During, and After
Public health distinguishes three levels of prevention, defined by WHEN they intervene relative to a disease's natural course. Primary prevention acts before disease onset, aiming to stop it from occurring at all — vaccination, health education, and safety regulations are classic examples. Secondary prevention acts once a disease process may have already begun but before it becomes symptomatic or severe, through early detection — cancer screening programs are the textbook case, catching disease at a more treatable stage. Tertiary prevention acts after a disease is already established, aiming to manage it, limit complications, and support functioning — cardiac rehabilitation after a heart attack is a typical example.
| Level | Timing | Example |
|---|---|---|
| Primary | Before disease occurs | Vaccination |
| Secondary | Early, before symptoms worsen | Cancer screening |
| Tertiary | After disease is established | Cardiac rehabilitation |
Beyond treating prevention as an individual medical matter, the World Health Organization's 1986 Ottawa Charter for Health Promotion reframed health promotion as a broader societal project, emphasizing action across multiple levels: building healthy public policy, creating supportive environments, strengthening community action, developing personal skills, and reorienting health services toward promotion rather than treatment alone. This reflects the same logic as the biopsychosocial model applied at a population scale — health is produced by social and environmental conditions, not simply delivered by individual medical encounters.
Common pitfall: treating "prevention" as a single undifferentiated idea. The THREE levels intervene at genuinely different points in a disease's course and call for different strategies — confusing early screening (secondary) with stopping disease before it starts (primary) leads to very different, and non-interchangeable, public health policies.