Influenza<unk> <unk>  or<unk>  effectiveness is the percentage reduction of disease cases in a<unk> ted group of people compared to an unvaccinated group. For example, a<unk>  or effectiveness of 80% indicates an 80% decrease in the number of disease cases among a group of<unk> ted people compared to a group in which nobody was<unk> ted. When a study is carried out using the most favorable, ideal or perfectly controlled conditions, such as those in a clinical trial, the term<unk> " is used. On the other hand, when a study is carried out to show how well a<unk>  works when they are used in a bigger, typical population under less-than-perfectly controlled conditions, the term<unk>  effectiveness" is used.<unk>  was designed and calculated by Greenwood and Yule in 1915 for the cholera and typhoid<unk> s. It is best measured using double-blind, randomized, clinical controlled trials, such that it is studied under "best case scenarios."<unk>  studies are used to measure several important and critical outcomes of interest such as disease attack rates, hospitalizations due to the disease, deaths due to the disease, asymptomatic infection, serious adverse events due to<unk> tion,<unk>  reactogenicity, and cost effectiveness of the<unk> .<unk>  is calculated on a set population (and therefore is not a constant value when counting in other populations), and may be misappropriated to be how<unk> ous a<unk>  is in all populations.
Vaccine efficacy
Bacterial phylodynamics
Transmission risks and rates
Vaccine equity
Timeline of human vaccines
Infection rate
Disease burden
Sociality and disease transmission