Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 17 1 2025 02 05 1 18 Delaram Doroud Department of Immunotherapy and Leishmania Vaccine Research, Pasteur Institute of Iran, Tehran, Iran Mojtaba Daneshi Department of Animal Sciences, Center for Nutrition and Pregnancy, North Dakota State University, Fargo,USA Fatemeh Kazemi-Lomedash Biotechnology Research Center, Department of Biotechnology, Pasteur Institute of Iran, Tehran, Iran Zohre Eftekhari Biotechnology Research Center, Department of Biotechnology, Pasteur Institute of Iran, Tehran, Iran 2024 07 13 2025 01 08 Following the worldwide spread of Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2), there is a vital requirement for safe and effective vaccines against Coronavirus disease 2019 (COVID-19). Therefore, several vaccine-candidate platforms have been designed, tested, and developed. Based on guidelines, preclinical studies are recommended to assess the safety and potency of COVID-19 vaccines in appropriate in vitro and in vivo settings. These studies provide essential information to describe the potential toxic properties of a vaccine and the formulation of vaccine agents during the preclinical trial phase. In toxicology studies, several factors must be considered, such as the appropriate animal species and strains, dosing timetable, mode of administration, time of sampling for biochemistry and antibody evaluation, and necropsy. Pharmacokinetic/ biodistribution studies are not usually required for infectious disease prophylaxis vaccines unless the vaccine contains a novel substance. Evaluating their biodistribution is crucial for newly developed vaccines, such as lipid nanoparticles –messenger RNA (LNP-mRNA), DNA, and Viral vectors in non-replicated (VVnr), or recombinant virus vaccines. The review highlights the importance of preclinical studies in assessing the safety and efficacy of vaccine candidates. This guidance is essential for researchers and manufacturers to design effective vaccines that can progress to clinical trials safely. https://ijm.tums.ac.ir/index.php/ijm/article/view/4911 https://ijm.tums.ac.ir/index.php/ijm/article/download/4911/1736