Phase 1 Overview

This is the first time a new vaccine or medicine is tested in humans; it will usually be given to a small group of healthy volunteers, or it may be tested on patients who have the condition it is designed to treat. The principal objectives in phase I are to ensure the new vaccine or medicine presents no major safety issues, and to see clear evidence that it can reach the targeted body area and remain there long enough to deliver its potential benefits. We also seek to gain preliminary evidence the vaccine or medicine can offer therapeutic value or help to prevent the disease in question.

Phase 2 Overview

At this stage, the potential vaccine or medicine is usually tested to understand the effectiveness against the disease it is designed to treat and appropriate dosing levels. The performance of the medicine in one group of patients may be compared against another group of patients receiving a placebo (a treatment that looks the same as the potential new medicine but has no active ingredients) or an existing treatment.

Phase 3 Overview

This phase consists of a much larger and potentially longer trial, often involving hundreds or possibly thousands of participants from a range of different countries. The principal objectives in phase III are to demonstrate the safety and effectiveness of the new vaccine or medicine in the typical patient likely to use it; confirm effective dosing levels; identify contraindications; build knowledge of the benefits of the vaccine or medicine and compare them with any risks; and compare results against any currently achieved by existing treatments. Regulators will determine how a new product should be used and which patients should qualify for it based on all the evidence from clinical and pre-clinical studies.