Vaccination: principles, history, safety, and impact

Vaccination and immune system adaptive priming

Vaccination is the administration of a vaccine to help the immune system develop immunity against disease. It works by artificially activating adaptive immunity through “priming” with an immunogen (a component of the vaccine), so the body can mount a faster and more effective immune response upon later exposure to the real pathogen. Vaccines may contain weakened live organisms, killed organisms, or specific proteins/toxins derived from the disease-causing agent, and they are often given before infection to build future protection. This adaptive priming differs from passive immunity, which provides immediate protection via transferred antibodies (for example, through breastfeeding). Vaccination can also be used after exposure for some diseases (e.g., smallpox post-exposure vaccination) to reduce severity or provide some protection. While vaccination generally produces lasting effects, it typically takes weeks to develop, and some individuals experience vaccine failure—most commonly when their immune systems do not generate the expected antibody response—often due to individual variation rather than a defective vaccine.

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Vaccine composition: weakened pathogens or proteins/toxins

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