What Is a Vaccine Trial?

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  • Written By: Andrea Cross
  • Edited By: PJP Schroeder
  • Last Modified Date: 25 October 2019
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Before any vaccines are approved and licensed for use on the public, they must go through vaccine trials. A vaccine trial is a form of clinical trial that is carried out to ensure that the medicine is both safe for use on humans and that it produces the expected protection from a particular virus, such as influenza. In order to become a licensed vaccine, a product must pass certain levels, or phases, of testing. The entire process from start to finish often takes a number of years and can cost millions of dollars. Usually, these trials are performed by certified research organizations at the behest of pharmaceutical companies.

Preclinical vaccine trials are performed before a vaccine trial can be carried out using human subjects. These trials can include testing the vaccine as part of a computer simulation, on cultured tissue in the laboratory, and on animals, including mice, rabbits, and monkeys. Although not always a useful reflection of how the potential vaccine will eventually work in humans, the purpose of this trial is to help determine the basic safety and efficiency of the drug.


If the vaccine passes the preclinical phase, then the drug passes through to phase one of the vaccine trial. This phase is carried out on human beings who have volunteered with informed consent to be tested. In the first phase, the volunteers are generally comprised of a relativity small group of healthy individuals. These people are chosen in large part based on their low risk of exposure toward the particular virus. The patients are administered the vaccine and then observed and tested to determine a number of results including antibody production, side effects, and varying dosage levels and schedules.

When the first phase is passed successfully, then the vaccine trial progresses to phase two. In this phase, a group of healthy volunteers that is both larger and who have varying degrees of risk and exposure to the virus are tested. This phase takes longer than the first, often a couple of years. Like the first phase, this trial also measures the pharmacokinetics and pharmacodynamics of the vaccine.

The third major phase of a vaccine trial uses volunteers, in even larger numbers, who are considered to be at high risk for the disease. By this time, the safety of the vaccine is fairly assured, and this trial mainly focuses on the drug's effectiveness and dosage fine-tuning. This trial phase tends to be the most expensive and takes the greatest amount of time, often three to five years. Several cycles of the trial may be carried out to confirm any results.

In order to successfully pass this phase, the clinicians must adhere to very strict protocol and documentation requirements. The trial must be carried out in a particular, designated way that is reviewed and audited. Methods of testing, including random testing, placebo, and double-blind testing, obtain the most accurate results possible. Once a vaccine has successfully passed all the prerequisite phases, it can be licensed for use.


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