Observational studies and the difficult quest for causality: lessons from vaccine effectiveness and impact studies
Observational studies and the difficult quest for causality: lessons from vaccine effectiveness and impact studies
Although randomized placebo-controlled trials (RCT) are critical to establish efficacy of vaccines at the time of licensure, important remaining questions about vaccine effectiveness (VE)—used here to include individual-level measures and population-wide impact of vaccine programmes—can only be answered once the vaccine is in use, from observational studies. However, such studies …