evidence: How are vaccine trials typically designed? Vaccine trials are typically tested through a study design called a randomized, double-blind and placebo-controlled trial. This means that participants are randomly assigned to receive either the experimental vaccine or a placebo. A placebo is an inactive injection that mimics the real experience to the patient. In the case of the vaccine, the placebo would be an injected salt water solution or something similar. The person receiving the treatment and the care provider giving the treatment do not know which group the participant belongs—whether the placebo or the treatment group. This type of trial helps minimize bias and makes the results more accurate because no one can alter results, intentionally or unintentionally, based on what they believe will work best. Data need to be collected on people with and without the vaccine so that the groups can be compared to determine if the vaccine is better than receiving nothing (the placebo).