The extent to which a specific health care treatment, service, procedure, program, or other intervention produces a beneficial result under ideal controlled conditions is its:

a. Effectiveness

b. Efficacy

c. Efficiency

d. Effect modification

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Ans: b. Efficacy

v  Efficacy (Potency) is the extent to which a specific intervention, procedure, or service produces the desired effect, under ideal conditions (controlled environment, lab circumstances). An efficacy study asks the question, "Does the vaccine work?"

v  Effectiveness is the extent to which a specific intervention, procedure, or service produces the desired effect, under ordinary conditions (real life, not controlled). an effectiveness study asks the question "Does vaccination help people?"

v  Efficiency is the ratio of the output to the inputs of any system. When outputs > inputs, then system is highly efficient.

Eg:

Vaccine efficacy shows how effective the vaccine could be given ideal circumstances and 100% vaccine uptake; 

Vaccine effectiveness measures how well a vaccine performs when it is used in routine circumstances in the community

Note:

Clinical Trial Phase I :  Safety Trial

Clinical Trial Phase II: Immunogenicity Trial

Clinical Trial Phase III: Efficacy Trial

Clinical Trial Phase IV: Effectiveness Trial