Which of the following best describes inactivated vaccines?

• A. They contain killed microorganisms that cannot replicate in the host.
• B. They provide lifelong immunity with a single dose.
• C. They use live, attenuated (weakened) forms of the pathogen.
• D. They are incapable of inducing an immune response.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand what an inactivated vaccine is. Inactivated vaccines contain microorganisms that have been killed or inactivated so they cannot replicate or cause disease in the host.
2. Step 2: Compare inactivated vaccines to live attenuated vaccines. Live attenuated vaccines use weakened but still living forms of the pathogen that can replicate to a limited extent, whereas inactivated vaccines cannot replicate at all.
3. Step 3: Consider the immune response generated. Inactivated vaccines are capable of inducing an immune response, but often require multiple doses or boosters to maintain immunity, unlike some live attenuated vaccines which may provide longer-lasting immunity with fewer doses.
4. Step 4: Evaluate the options given in the problem. The correct description of inactivated vaccines is that they contain killed microorganisms that cannot replicate in the host.
5. Step 5: Confirm that statements about lifelong immunity with a single dose or inability to induce an immune response do not apply to inactivated vaccines, as these are characteristics of other vaccine types or incorrect.