Stimulating an immune response
Vaccines expose the immune system to recognizable antigens, stimulating antibody and cellular responses and potentially establishing immune memory. A later encounter with a related pathogen can then produce a faster response.
Different vaccines present antigens through approaches including attenuated organisms, inactivated organisms or selected components. The degree and duration of protection depend on the vaccine, its administration and the recipient. Administration is an action; protection is an outcome that must be evaluated.
From cowpox to laboratory vaccines
Edward Jenner investigated cowpox and protection against smallpox in the late eighteenth century. During the nineteenth century, microbial research supported work on additional preventive methods, including investigations by Pasteur and his collaborators.
Rabies vaccination after exposure in 1885 combined animal research, preparation methods and clinical administration. Subsequent development introduced larger trials, production controls and public-health evaluation, creating conditions different from those of early individual experiments.
Routine programmes and public health
Population programmes depend on production, transport, storage, trained staff and records as well as the vaccine itself. Routine services organize individual administrations into continuing public-health work.
Smallpox eradication and the use of polio and measles vaccines involved surveillance, delivery and evaluation of coverage. Effects on infection, transmission and severe illness differ between pathogens and vaccines, so these outcomes require separate assessment.
Active immunity and evaluation
Vaccination usually develops active immunity through the recipient’s own immune system. Passive immunization instead supplies antibodies already produced elsewhere, with a different mechanism and duration of protection.
Evaluation considers safety, protection and performance in use. Evidence about a product, the ability of services to reach people and changes in disease within a population answer different questions about a vaccination programme.