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 principle 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.  

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.

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 principle 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.

Monitoring is overseen by our Global Safety Board (GSB), which is chaired by our chief medical officer and made up of senior physicians and scientists. Part of its remit is to review the information on the safety of our products as reports come in from patients and prescribers on the use of the medicines. All the board's decisions are guided by the need to ensure that the benefits of our vaccines and medicines always outweigh any risks. We continue to monitor patients' responses to our medicines through reports and regulator reporting systems. We follow this information to fully understand a new vaccine or medicine's effectiveness. We also look for any adverse effects that may only become apparent as more patients use a treatment.