> These are the same thing. The only way to demonstrate the efficacy of a vaccine is if the control group gets sick, otherwise there can't be a relative improve

> These are the same thing. The only way to demonstrate the efficacy of a vaccine is if the control group gets sick, otherwise there can't be a relative improvement. That's simply not true. A vaccine efficacy study specifically validates how well the introduction of a vaccine prevents disease, it does nothing to show the specific link between disease and the pathogen itself. Prior studies are needed to link the pathogen to disease, and the most accurate way to do this is to first isolate the pathogen then show that introducing it to a novel population recreates the disease. After symptoms show up, if the pathogen can again be isolated from the newly infected hosts you have a pretty strong case for causation. Moving on to reproducing the results in follow up studies would go a long way. At that point you know the likely pathogenic cause and can move on to developing a vaccine based on that pathogen and run efficacy studies to see how well the vaccine works to prevent infection, disease, or transmission.