The three levels of prevention

Injury prevention borrows a ladder from public health. Primary prevention stops the injury happening at all. Secondary prevention limits the harm once the event is under way, in the seconds it takes. Tertiary prevention is the care, rehabilitation and support that follow, which decide how much of the damage is permanent. CDC describes the science of injury control as running across all three, from primary prevention through treatment and rehabilitation.

Primary: stop it happening

Primary prevention removes the hazard, or removes people from it. A speed limit that keeps impact forces survivable, a fence between a toddler and a pool, a cookstove that does not tip, a guard rail, a law against driving under the influence, a covered well: none of these depend on anyone reacting correctly on the day.

This is where the field's biggest wins have come from, and it is where WHO's prevention packages concentrate. It is also the level most likely to be invisible when it works, because nothing happens and there is nothing to count.

Secondary: limit the harm in the event itself

Some crashes, falls and fires will happen anyway. Secondary prevention is everything that changes how much harm the event does while it is happening: the seat belt, the airbag, the helmet, the child restraint, the crumple zone, the soft surface under the play equipment, the smoke alarm that wakes a household in time.

These measures accept that the event has begun and work on the energy reaching the body. WHO's figures for helmets, seat-belts and child restraints are all measures of this kind — they do not reduce the number of crashes, they reduce what a crash does to a person.

Tertiary: change what the injury leaves behind

Tertiary prevention starts the moment the event ends. It covers bystander first aid, the call for help, the ambulance, the trauma system, the surgery, and then the rehabilitation, the assistive products and the removal of barriers that decide whether someone returns to work and to life.

WHO makes the case for treating this as prevention rather than as aftermath: delays of minutes after a road crash change who lives, and organised trauma care, rehabilitation and access to assistive products change how much disability an injury leaves. CDC's account of the field says the same — injury control reaches from primary prevention through treatment and rehabilitation.

Using the three levels in practice

The reason to hold all three in mind is that a programme built only at one level is fragile. Helmet campaigns without safe road design, or trauma centres without speed management, each leave most of the problem untouched.

The levels also map onto the time before, during and after an event, which is what makes them fit together with the Haddon matrix: the matrix is the same three moments laid across the factors that shape them. Read the two together and a prevention plan usually writes itself.

Sources

CDC — Injury Prevention, Violence Prevention, and Trauma Care: Building the Scientific Base (MMWR Supplement 60(4), 2011) — www.cdc.gov, read 15 September 2026.
WHO — Injuries and violence (fact sheet) — www.who.int, read 15 September 2026.
WHO — Road traffic injuries (fact sheet) — www.who.int, read 15 September 2026.
CDC — Preventing TBI — www.cdc.gov, read 15 September 2026.