Step 1: Concept
Vaccines are biological preparations that provide active acquired immunity to a particular infectious disease and are categorized as bacterial or viral.
Step 2: Meaning
Bacterial vaccines use weakened or killed bacteria, while viral vaccines use weakened or killed viruses.
Step 3: Analysis
BCG (Tuberculosis), DPT (Diphtheria, Pertussis, Tetanus), and Plague vaccines are bacterial. Yellow fever is caused by a virus (Flavivirus), and its vaccine is a live attenuated viral vaccine.
Step 4: Conclusion
Therefore, the Yellow fever vaccine is the correct example of a viral vaccine.
Final Answer: (A)