The Trials: Sequence of Events

Vaccines are supplied by the companies that develop them. They are then tested through a series of steps to ensure that the final product is both safe and effective. All candidate vaccines go through the following stages, with only the best progressing to the next step:

• Laboratory and animal tests, followed by studies to test safety and ability to activate the immune system in a small number of volunteers (Phases I and II).
• A large-scale efficacy trial (Phase III), which will show whether the vaccine really protects against infection and/or disease. Only when a vaccine proves both safe and effective in a Phase III trial will it be considered for use in the public.