SAMUEL ASHFIELD / SCIENCE PHOTO LIBRARY SAMUEL ASHFIELD / SCIENCE PHOTO LIBRARY
Vaccination. Doctor injecting a vaccine into the arm of a patient. Vaccination is a process in which dead or weakened pathogens are injected into a patient in order to prime their immune system against them. This means that if the patient encounters the active pathogen, his or her immune system is more able to combat the infection. Several diseases have been controlled by the mass vaccination of populations.
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