Vaccine development is a complex and time-consuming process that differs from the development of conventional drugs. Indeed vaccines are intended for use in healthy individuals as a preventive measure whereas conventional drugs are aimed at the treatment of a condition. Vaccine clinical trials focus on demonstrating prevention of a disease which implies that a higher number of subjects will be required than for traditional drug trials.
Before a vaccine is licensed and brought to the market, it undergoes a long and rigorous process of research, followed by many years of testing. On average, the period for vaccine development is 12 to 15 years and will involve the following phases:
1. Pre-Clinical Trials
In vaccine development, the first step to identifying a vaccine candidate is the pre-clinical development stage which goal is determining a vaccine’s ultimate safety profile. During this stage the researchers will carefully select the antigen and appropriate technologies and both in vitro and in vivo tests will be performed. The information collected from these studies will be vital to begin safe clinical trials.
2. Phase I clinical trials
Phase I trials involve a small number of healthy volunteers (20-50). The researchers will test the candidate vaccine for the first time in humans in order to evaluate its safety, determine a safe dosage range, and identify vaccine-related side effects. This is achieved by comparing the vaccine with a control or an inactive substance called placebo (e.g. saline solution).
Phase I trials can also provide initial data on the dose and the time needed between vaccinations that will lead to an optimal immune response. This first phase of the clinical trials lasts 12 to 18 months.
3. Phase II clinical trials
If the candidate vaccine presents optimal results in phase I, it will then undergo Phase II trials during which the candidate vaccine is administered to a larger group of people (100-300) to further evaluate its safety and immunogenicity.
This phase will explore more deeply the right dose and administration schedule and can last 2 or more years.
4. Phase III clinical trials
The most promising vaccine candidates move into Phase III enrolling 3,000 to 50,000 subjects. The goal of this phase is to conduct a large-scale safety and efficacy study in the relevant patient population to which the vaccine is aimed. Moreover during this phase concomitant administration with other vaccines will be tested.
Phase III clinical trials can last 3 to 5 years.
5. Phase IV or Pharmacovigilance
Once a vaccine has been marketed, pharmacovigilance activities take place in order to carry on a strict safety supervision of the vaccines and detect, assess, understand, prevent and communicate any adverse events following immunisation, or of any other vaccine- or immunisation-related issues. Long-term follow-up trials are often conducted to provide evidence that the protection offered by the vaccine is long-lasting