What happens when an individual's immune system prevents transmission?

• A. It prevents illness.
• B. It increases susceptibility.
• C. It has no effect.
• D. It causes more infection.

Answer: (A)

A strong immune response that stops transmission usually means the pathogen is neutralized before it can establish disease, so the person does not develop illness. When the body quickly controls or eliminates a pathogen, symptoms don’t appear and the person remains healthier. This same immune activity also tends to reduce how much pathogen is shed, lowering the chance of spreading to others. So the best description is that illness is prevented for the individual. The other options don’t fit because they imply increased vulnerability, no effect, or more infection, which contradict the protective action of a capable immune response.