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How does a clinical trial work?


PHASE 1 - Clinical Studies


Phase 1 studies test the safety of a product. This means seeing if there are side effects, and whether the human body can tolerate the vaccine or antibody. The experimental product is often compared to a group that receives a placebo, a substance such as sterile saltwater that has no active ingredients. These studies are conducted with a small group of people (usually less than 100) and typically last 12 to 18 months.


PHASE 2 - Clinical Studies


Phase 2 studies look at questions such as the maximum tolerated dose, the optimal schedule for giving the product (how many doses, and at what time intervals), and whether the immune system is having the desired responses. These responses can include the production of antibodies, the production of T cells, and other immune system markers. These studies are conducted with a medium-size population of volunteers (usually a few hundred to 1000) and the studies can last up to 2 years.


PHASE 2B - Clinical Studies


Phase 2b studies are a way to get an early look at whether the product is effective at preventing infection or disease. They are sometimes known as Proof of Concept or Test of Concept studies. A group of several thousand people who are at increased risk for infection or disease are enrolled, and the studies can last about 2-5 years. Based on the data from these studies, researchers can see whether the results seem favorable, supporting moving ahead to Phase 3. If the results are less favorable, it means that researchers can redirect their efforts and save the expenses of large Phase 3 studies.


PHASE 3 - Clinical Studies


Phase 3 studies are where researchers can ask the questions, “Does this product prevent new infections? Or if people do become infected, does the product help them control the infection so that it doesn’t become severe disease?” These studies involve many thousands of people, usually including some participants who are at increased risk for infection.


PHASE 4 - Clinical Studies


Phase 4 studies may take place after a product has been found to be effective in some populations, and are utilized to gather additional information about safety and effectiveness by testing the product in additional populations such as children or pregnant women. They are sometimes known as bridging studies, or post-licensure studies. These studies may be conducted on anyone seeking a prevention option from their physician.

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