Principles of Preventive Medicine: Levels of Prevention and Immunization

Abstract

Prevention is the foundation of public health, and preventive medicine seeks to protect, promote, and restore health by acting at every stage of the natural history of disease. This paper reviews the principles of preventive medicine, focusing on the levels of prevention and on immunization as a cornerstone of specific protection. A review-based approach is adopted, drawing on the standard texts of preventive and community medicine. The analysis sets out the natural history of disease and the levels of prevention that correspond to its stages, primordial prevention, which prevents the emergence of risk factors; primary prevention, comprising health promotion and specific protection, applied before disease occurs; secondary prevention, comprising early diagnosis and prompt treatment; and tertiary prevention, comprising disability limitation and rehabilitation, applied once disease is established. It then examines immunization, distinguishing active immunization by vaccines, live attenuated, inactivated, toxoid, and subunit or conjugate, from passive immunization by preformed antibodies, and describing immunization schedules, the concept of herd immunity, and the requirements of the cold chain. The study finds that the levels of prevention provide a comprehensive framework that matches interventions to the stage of disease, and that immunization is among the most effective of all preventive measures, capable, at sufficient coverage, of protecting whole populations and even of eradicating disease. It concludes that preventive medicine, structured by the levels of prevention and exemplified by immunization, is central to the protection of population health. Certainquantitative figures are illustrative. KEYWORDS: Preventive Medicine, Levels of Prevention, Immunization,Vaccines, Herd Immunity, Health Promotion, Natural History of Disease,Public Health