**Core Concept**
Lyophilized (freeze-dried) vaccines are a type of vaccine that has been dried using a process that removes the water content, allowing for easier storage and transportation. This process involves freezing the vaccine and then reducing the surrounding pressure to allow the frozen water to sublimate (change directly from a solid to a gas) without going through the liquid phase.

**Why the Correct Answer is Right**
Lyophilized vaccines typically do not include preservatives, as they are often inactivated or killed vaccines that have undergone a stabilization process to prevent degradation. The freeze-drying process itself acts as a preservation method, making preservatives unnecessary. Additionally, lyophilized vaccines often require reconstitution with a diluent before administration, which can help maintain their potency and stability.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect, as lyophilized vaccines may include stabilizers such as sugars, amino acids, or other compounds to help maintain their structure and prevent degradation.
* **Option B:** Incorrect, as lyophilized vaccines may include adjuvants, which are substances added to vaccines to enhance the immune response.
* **Option C:** Incorrect, as lyophilized vaccines may include buffers, which are substances added to maintain the pH of the vaccine and prevent degradation.

**Clinical Pearl / High-Yield Fact**
Lyophilized vaccines are often used for vaccines that require multiple doses, as they can be easily reconstituted and administered in a clinical setting.

**Correct Answer: B. Adjuvants. Adjuvants are not typically included in lyophilized vaccines.**