Microorganisms, Diseases and Immunity — Punjab Police previous year questions

Vaccination belongs to preventive medicine, and within it to specific protection at the level of primary prevention — action taken before the disease occurs at all. A vaccine introduces a killed, weakened or partial form of the pathogen, or its genetic instructions, so that the immune system makes antibodies and memory cells; if the real organism arrives later, the response is fast enough to stop illness. Where enough of the population is covered, transmission itself breaks down, which is herd immunity, and that is how smallpox was eradicated in 1980 and how the Universal Immunisation Programme and Mission Indradhanush work in India. Curative or therapeutic medicine treats disease that already exists, and social medicine studies the social and economic determinants of health; neither describes a vaccine. Hence option 3.