How are vaccines developed?

Vaccines are developed in multiple stages. First, the virus needs to be examined to determine the basic requirements for a possible vaccine. This information is then used as a basis for developing initial vaccines in the laboratory and selecting the most promising for use in preclinical studies. In preclinical studies, vaccines are tested in cell cultures and in animal models with the aim of ruling out serious side effects.

Then they are tested in humans in three different clinical phases. While these phases are usually completed sequentially, they were carried out to some extent in parallel in the case of Covid-19 vaccines. In the first clinical phase, vaccines are tested for basic safety. In the second phase, the dose levels are determined. And in the third phase, the vaccines are tested on large numbers of healthy volunteers (Pfizer/BioNTech: 44,000, Moderna: 30,000, AstraZeneca: 24,000) to assess their safety and efficacy. Such studies are discontinued if any serious and unexpected adverse events occur.

If a vaccine proceeds through these three clinical phases successfully, the manufacturer will submit an application, in Switzerland at Swissmedic, for official approval. After receiving approval, manufacturers continue in the context of a fourth clinical phase to gather and assess side effectsof their vaccines.

More information is available in this video released by Swissmedic.