" efficacy " how is it calculated? 

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The primary goal of most clinical trials is an evaluation of the efficacy of the drug being evaluated. Therefore, it is important to understand if study outcomes are a true reflection of a drug's "real-life" effectiveness. Clinical trials generally evaluate three types of outcomes: subjective, objective, and health-related. Clinical trials that use subjective measures as endpoints usually evaluate outcomes such as symptom scores, the need for rescue medication, and quality-of-life measures.

1. how is vaccine's "efficacy" calculated?

Two general types of studies are used to determine how well influenza vaccines work: randomized controlled trials and observational studies.
More about it here at CDC

2.  efficacy vs effectiveness

​Efficacy and effectiveness are related to each other, but they're not the same thing. Efficacy is just a measurement made during a clinical trial. 'Effectiveness is how well the vaccine works out in the real world,

3. evolution of immunization 

​Following current developments with the coronavirus, I began to research more about what scientists are doing to combat the disease and one of the main topics I found research are immunizations.

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