A review of the scientific literature on experimental toxicity studies of COVID-19 vaccines, with special attention to publications in toxicology journals

Since the reports of the first cases of COVID-19, in less than 5 years, a huge number of documents regarding that disease and the coronavirus (SARS-CoV-2), responsible for the infection, have been published. The tremendous number of scientific documents covers many topics on different issues directly related to COVID-19/SARS-CoV-2. The number of articles—including reviews—reporting adverse/side effects of the approved COVID-19 vaccines is considerable. A wide range of adverse/side effects have been reported in humans after COVID-19 vaccination: thrombotic events/thrombocytopenia, myocarditis/pericarditis, cutaneous reactions, immune-mediated effects, psychiatric adverse events, systemic lupus erythematosus, reproductive toxicity, and other miscellaneous adverse effects. In contrast, information on nonclinical studies conducted to assess the potential toxicity/adverse effects of the COVID-19 vaccines in laboratory animals, is comparatively very scarce. The present review was aimed at revising the scientific literature regarding the studies in laboratory animals on the toxic/adverse effects of COVID-19 vaccines. In addition, the investigations reported in those specific toxicology journals with the highest impact factors have been examined one by one. The results of the present review indicate that most nonclinical/experimental studies on the adverse/toxic effects of the COVID-19 vaccines and/or potential candidates showed—in general terms—a good safety profile. Only in some animal studies were certain adverse effects found. However, a rather surprising result has been the limited number of available (in the databases PubMed and Scopus) nonclinical studies performed by the companies that have been the largest manufacturers of mRNA vaccines in the world. It is assumed that these studies have been conducted. However, they have not been published in scientific journals, which does not allow the judgment of the international scientific community, including toxicologists.