Vaccine Development Phases
In vaccine development, the first step to identifying a vaccine candidate is the pre-clinical development stage. During this stage, the researchers carefully select the antigen and appropriate technologies, and then both in vitro and in vivo tests are performed. The information collected from these studies is vital to begin safe clinical trials.
Phase I clinical trials
Phase I trials involve a small number of healthy volunteers (around 20-50). The researchers 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.
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 (around 100-300) to further evaluate its safety and immunogenicity. This phase explores more deeply the right dose and administration schedule and can last 2 or more years.
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 at which the vaccine is aimed. Moreover during this phase concomitant administration with other vaccines is tested. Phase III clinical trials can last 3 to 5 years. 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.