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(*) Denotes "Phase I/II" stage announcement
Explanation of the Phases
In the beginning phase of vaccine development, the pathogen in question, the "antigen" needs to be identified. This requires a thorough understanding of the structure and function of the antigen in order to move to the next phase.
In this phase, the antigen is either killed, severely weakened, or broken into fragments. This allows the host to recognize the functional parts of the virus with the goal of naturally developing antibodies which attack the antigen, but without a true infection.
Prior to human testing, the vaccine is studied and tested in animal trials. Researchers are determining whether the alteration of the antigen maintains its ability to properly produce antibodies and the appropriate immune response. Adjuvants are also studied in this phase.
This is the first of three phases of human trials focusing on safety and dose tolerance.
Phase II continues the research of Phase I but with a larger group of participants. This is sometimes divided into a Phase IIA and Phase IIB.
"...multiple variables associated with the host immune response are considered. Determinants of clinically applicable vaccine regimens are also included, such as the dose and number of doses, sequence/interval between doses, and route of administration. Vaccine efficacy may be evaluated using well-defined surrogate parameters. Most of these clinical trials include parallel group comparisons with placebo/active control groups."
Proof of Concept
With the successful conclusion of Phase II, a Proof of Concept or PoC is ensured to "demonstrate the immunogenicity of the relevant active component(s) and the safety profile of a candidate vaccine within the target population and to define the optimal dose, initial schedule, and safety profile of a candidate vaccine"
In this phase, the participant quantity is increased to several thousand individuals and crucial decisions/data collection is made to confirm market approval.
Completing Phase III, all information gathered during the testing and study of the vaccine candidate is filed with regulatory authorities. "The WHO and each regulatory authority have their own guidelines to ensure the quality of the information provided"
Upon approval, the vaccine is candidate receives marketing approval. Studies continue after the marketing of the vaccine to continue gather data on safety and efficacy.