**Core Concept**
Neomycin is an aminoglycoside antibiotic that inhibits protein synthesis by binding to the bacterial 30S ribosomal subunit. It is commonly used as a preservative in vaccines to prevent bacterial contamination.

**Why the Correct Answer is Right**
Neomycin is added to vaccines to prevent the growth of bacteria, particularly those that can cause disease in humans. This is especially important for live, attenuated vaccines that contain weakened but still viable pathogens. By adding neomycin, the risk of bacterial contamination and subsequent disease transmission is significantly reduced. Neomycin's mechanism of action is to bind to the 30S ribosomal subunit, thereby inhibiting the initiation complex of peptide formation and ultimately leading to the inhibition of protein synthesis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the use of neomycin in vaccines.
**Option B:** Neomycin is not used to prevent viral contamination in vaccines.
**Option C:** This option is incorrect as neomycin is not used to prevent fungal contamination in vaccines.

**Clinical Pearl / High-Yield Fact**
It's essential to note that neomycin is not without risks, and its use in vaccines has been associated with hypersensitivity reactions and renal toxicity. However, the benefits of using neomycin as a preservative in vaccines outweigh the risks, making it a crucial component in preventing bacterial contamination.

**Correct Answer:** C. Inactivated Poliovirus Vaccine.