CDISC-Gloss – The proportional comparison of infection rate or other disease endpoints between vaccinated and unvaccinated groups measured in randomized controlled trials. Efficacy is a measurement made during a clinical trial; effectiveness is how well the vaccine works out in the real world. [After Greenwood et al., Proc R Soc Med. 1915; 8 (Sect Epidemiol State Med): 113-194, The Statistics of Anti-typhoid and Anti-cholera Inoculations, and the Interpretation of such Statistics in general. After Piero Ollario, The Lancet Infectious Diseases, Feb 17th, 2021] See also vaccine effectiveness, effectiveness, efficacy, randomized controlled trial (RCT).