The immune system is a critical defence mechanism that can detect and destroy an invading pathogen. Immunization prevents disease by allowing the body to respond to an attack more quickly and by boosting the immunological response to a specific pathogen. Although an ideal vaccine is simple to define, few practical vaccines come close, and many creatures for which a vaccination is the only realistic preventive strategy in the foreseeable future lack vaccines.
Vaccines use adaptive immunity and memory to expose the body to antigens without causing disease, so that when a live pathogen infects the body, the immune system responds quickly and the pathogen is prevented from causing disease. The delivery of a vaccine to aid the immune system in developing protection against a disease is known as vaccination. Vaccines comprise a weakened, live, or deceased microbe or virus, as well as proteins or toxins from the organism. They aid in the prevention of infectious disease illness by increasing the body's adaptive immunity. Vaccines are one of the most significant achievements in world health and development.