Which term refers to preparations that contain suspensions of microorganisms, typically derived from animals, and are used to elicit immunity?

• A. Vaccines
• B. Anistreplase
• C. Fentanyl
• D. Adenosine

Answer: (A)

Vaccines are preparations that introduce antigens to the immune system in order to train it to recognize and fight off future infections. Describing them as suspensions of microorganisms, typically derived from animals, captures the traditional idea of presenting a harmless or inactivated form of a pathogen so the body builds specific immunity without causing disease. This exposure prompts both antibody production and cellular memory, so when real pathogens are encountered later, the immune system responds quickly and effectively.

Other options are not about immunity: one is a thrombolytic used to dissolve clots, another is an opioid analgesic, and the last is an antiarrhythmic drug.