Which of the following best describes active immunity?

Active immunity is characterized by the immune system's direct response to a pathogen or vaccine, leading to the development of specific antibodies and memory cells. This process involves the body's own immune response to recognize and combat foreign invaders.

The statement about immunity developed through vaccines refers to the administration of a weakened or inactivated form of a pathogen or pieces of the pathogen. This exposure prompts the immune system to produce antibodies and memory cells without causing the disease, leading to active immunity.

The description of immunity attained through exposure to pathogens highlights another aspect of active immunity, where the body encounters a pathogen in its natural form. This encounter stimulates the immune system to develop a robust response, creating the necessary antibodies and long-term memory cells for future protection against the same pathogen.

Therefore, the choice that includes both immunity developed through vaccines and immunity attained through exposure to pathogens accurately encompasses the full concept of active immunity, illustrating how both scenarios contribute to the development of immunity that lasts over time. This comprehensive understanding reinforces the critical role of the body's immune system in protecting against disease.