To solve this conundrum, the first step is to have a clear overview of the development stages of a vaccine ensuring its quality, safety and effectiveness, as shown below.
1) The exploratory stage consists of basic research screening the pathogen for potential target antigens, determining the most suitable vaccine type and formulation, and investigating the manufacturing process in detail.
2) Once promising vaccine candidates are identified, they are narrowed down in pre-clinical studies which are conducted in vitro (tissue/cell-culture systems) and/or in vivo (animal models) to evaluate their safety (including the best administration route and dosing) and immunogenicity.
3) At this point, regulatory authorities (RA) need to make sure that the vaccine’s quality profile is satisfying so that it can safely move on to clinical studies, which include 3 phases:
4-5) After a successful phase III trial, a meticulous evaluation of the vaccine’s test results and manufacturing conditions (presented in a “marketing authorization” application) is performed by RAs to confirm the safety and quality of vaccine batches intended for market release. Ultimately, a vaccine will only be approved for manufacturing if its benefits are considered to outweigh its risks.
6) Finally, following approval, safety monitoring/pharmacovigilance (= phase IV trials) is continuously performed to ensure that any possible risk is detected and managed as fast as possible. In addition, every new batch of vaccine is tested for quality and safety before its commercial release.