When considering opportunities and methods to address human and animal health problems, three stages of prevention are generally recognized:
Primary prevention focuses on avoiding development of a disease by preventing it before exposure. Examples of primary prevention strategies include immunization programs, health education, and smoking cessation interventions. Because disease is largely avoided by these strategies, primary prevention is generally regarded as the most cost-effective form of prevention.
Secondary prevention focuses on early disease detection and intervention, ideally before the onset of clinical signs. Examples include screening programs against specific forms of cancer, postexposure rabies prophylaxis, tuberculosis skin tests, and infectious disease contact investigations.
Tertiary prevention focuses on managing disease after diagnosis to stop or slow progression. Examples include antimicrobial treatment, hypertension drugs, heart attack and stroke rehabilitation, and screening for complications. Because this stage focuses its efforts after disease is established, tertiary prevention is the least cost-effective form of prevention.