These are some of the stages a vaccine will have gone through before use:
- Reviewing what has been done before.
- Theoretical development or innovation: coming up with a new idea, or a variation on an existing idea.
- Laboratory testing and development. This involves 'in vitro' testing using individual cells and 'in vivo' testing, often using mice. The vaccine has to pass rigorous safety tests at this stage, and demonstrate that it works in animals.
- Phase I study – an initial trial involving a small group of adult participants (up to 100 people). This is carried out to make sure that the vaccine does not have major safety concerns in humans, and also to work out the most effective dose.
- Phase II study – a trial in a larger group of participants (several hundred people). Phase II trials check that the vaccine works consistently, and look at whether it generates an immune response. Researchers also start looking for potential side effects.
- Phase III study – a trial in a much larger group of people (usually several thousand). Phase III trials gather statistically significant data on the vaccine's safety and efficacy (how well it works). This means looking at whether the vaccine generates a level of immunity that would prevent disease, and provides evidence that the vaccine can actually reduce the number of cases. It also gives a better chance of identifying rarer side effects not seen in the phase II study.
- Licensing – expert review of all trial data by the UK government (through the Medicines and Healthcare products Regulatory Agency - MHRA) At this stage the regulators check that the trials show that the product meets the necessary efficacy and safety levels. They also make sure that, for most people, the product’s advantages far outweigh the disadvantages.
- Phase IV studies – post-marketing surveillance to monitor the effects of the vaccine after it has been used in the population. These may be requested by a regulatory body, or carried out by the pharmaceutical industry.
