 How do we develop a new vaccine? After lots of laboratory work, how do we know it is ready to get tested in humans? And then, how do we know whether or not it works? We test new vaccines in clinical trials to determine that they are both safe and effective before they get licensed in the US. Stick with us, this is going to be interesting. And, although this applies to all kinds of drugs and vaccines, we're going to focus here on vaccines used for prevention of a specific type of infection. The first thing to know is that a lot of testing is done before a vaccine ever gets tested in humans. There is a long process of development in the laboratory and testing both for safety and for protection in animal studies. After we have a vaccine that looks both safe and promising in preventing infection in the laboratory, we begin testing in humans. Because we don't know whether or not the vaccine will work, we begin a very structured set of studies called clinical trials. These studies involve healthy volunteers who are told in detail about how and why this vaccine is being tested and about any potential harm. This educational process is a process called informed consent and goes on before and during the trial. There is a continual discussion that happens between the researchers and the study volunteers describing the study, informing the volunteers about any new information that happens at any time during the study and answering all questions that the volunteers have. The study staff also determine whether the volunteer meets all the eligibility criteria to participate, which involves physical exams and blood tests. Next, we start what is called a randomized double-blinded clinical trial. What that means is that after volunteers enroll in a study, a computer randomly decides whether they will get the vaccine or whether they will get the placebo, which is usually just salt water. We do this to be able to separate outside effects that are due to the vaccine from those that are just happening to people in the community at the same time, like the rate of cold symptoms or headaches. And we double-blind, meaning neither the participant nor the study staff know who is getting which type of injection. That prevents both the volunteers and the staff from over or under reporting symptoms. We advise participants to tell us about everything that is happening to them. Before a vaccine is licensed by the U.S. Food and Drug Administration, it usually goes through three phases of clinical trials, each of which has a specific purpose. Phase 1 trials, which can last up to two years, compares the safety, does the vaccine cause any side effects, and tolerability, does the injection hurt, and for how long. In this phase of studies, scientists are also gathering information about the body's immune response to the vaccine to see whether it is a promising approach to preventing the specific infection. Phase 1 trials do not determine whether or not the study product is actually doing what we hope it will do. Phase 2 trials, which can last longer than two years, will confirm the safety in a larger group of volunteers and focus on the best dose and the best timing of vaccinations to produce the strongest immune response. Promising vaccines that are safe and generate a strong immune response move into phase 3 trials. These are the largest trials and compare the rate of infection in the vaccine and placebo groups. This will tell us whether the vaccine is able to prevent infection, and if so, if it is effective in all of the volunteers or only a subgroup, like younger volunteers or women. Along with the safety data that is collected in all phases of vaccine studies, this efficacy data is used by the FDA to decide if the vaccine should be licensed and if so, for whom it is recommended. In the best case scenario, it could take 6 to 10 years for a promising vaccine to move from phase 1 testing to real-world distribution. Often, it takes longer. But clinical trials are absolutely necessary to determine that a vaccine is safe and effective in preventing new infections. This video has been provided to you by Eureka Science in collaboration with Bridge HIV. To stay in touch with Eureka Science, like us on Facebook, follow us on Twitter, or subscribe to this YouTube channel, or visit us at eurekascience.org. Thank you for watching!