Vaccination: purpose, methods, safety, and history

Vaccination and immune system adaptive immunity

Vaccination is the administration of a vaccine to help the immune system develop adaptive immunity against disease. Vaccines contain weakened live organisms, killed organisms, or specific proteins/toxins from the pathogen. By priming the immune system with an immunogen, vaccines stimulate adaptive immune responses that reduce the risk of illness from infectious diseases. When enough people in a population are vaccinated, herd immunity can protect even those who cannot be vaccinated (such as some immunocompromised individuals), because transmission is less likely. Vaccines can be given before infection to build long-term protection, though some are also used after exposure to reduce disease severity or provide partial protection (e.g., post-exposure smallpox and rabies strategies). Most vaccines take weeks to produce protection, unlike passive immunity, which provides immediate antibodies. Vaccine failure can occur when a vaccinated person still contracts the disease, often due to individual differences in immune response rather than a defective vaccine. Vaccination differs from inoculation/variolation, which uses unattenuated pathogens and historically carried a higher risk of causing severe disease.

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Vaccine components: weakened pathogens or proteins/toxins

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