Summary of 2025 Society of Toxicology Workshop "Vaccine Toxicology in the Post-COVID Era".

Nonclinical safety studies to support clinical development and registration of vaccines is a specialized area within pharmaceutical regulatory toxicology. Toxicology testing for vaccines has been required since the mid-1990s, starting with the publication of the European Medicines Evaluation Agency (EMEA) Note for guidance on preclinical pharmacological and toxicological testing of vaccines (CPMP/SWP/465/95), which was later withdrawn in 2016. Toxicological assessment of vaccines is, in many respects, quite distinct from that required for small molecules or other categories of biological drugs. The coronavirus disease-19 (COVID-19) pandemic brought with it rapid advances in vaccine technology, such as the widespread introduction of mRNA vaccines, as well as changes in regulatory agency review procedures to accelerate clinical development. This paper provides a summary of the presentations given during the Coalition for Epidemic Preparedness Innovations (CEPI) workshop at the 2025 Society of Toxicology annual meeting. The workshop focused on several current aspects of toxicology studies for vaccines in the post-COVID era, including regulatory perspectives on vaccine nonclinical safety testing, and impact on development of lipid nanoparticles (LNPs), mRNA vaccines, and novel adjuvants. The conclusion from the workshop was that it is time for a review and update of vaccines guidance documents to incorporate learnings from the approximately last 35 years.