Genetic Stability of Smallpox Virus Key to Eradication Success

Steps:

• Evaluate options based on virology of variola virus: human-specific, non-latent, DNA-based stability.
• Eliminate B and D as they describe latency or high mutation, which variola lacks.
• Confirm A as a factor but not the sole reason; stability ensured vaccine efficacy.
• Select C as it directly enabled consistent, lifelong immunity via unchanging antigens.

Why C is correct:

• Variola's DNA genome is stable with low mutation rates, allowing a single vaccine formulation to induce durable immunity without antigenic drift, per principles of viral evolution.

Why the others are wrong:

• A: True for no animal reservoir, but eradication required stable vaccine targets too.
• B: Smallpox causes acute infection without latency or reactivation.
• D: Contradicts C; variola's stability prevented mutations that could evade vaccines.

Final answer: C