These previous attempts at mRNA vaccines initially produced good results. But, when exposed to the wild version of the virus, many of the subjects became ill and died. The speculation was that these vaccines produced Antibody Dependent Enhancement. In short, these vaccines seemed to cause the immune system to wildly over-react, often resulting in death. Will these vaccines do the same? Nobody knows.
Add to this the fact that Anthony Fauci, and others pushing the jab, own patents in parts of these vaccines, and it is legitimate to be concerned about conflicts of interest."
https://cuencahighlife.com/the-case-for-vaccine-hesitancy-backed-by-science/I guess human bodies are more complex and adaptable, so skipping successful animal trials was "work around".
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC525089/https://www.nature.com/news/2005/050110/full/050110-3.html#ref-CR1 https://www.pnas.org/content/102/3/797https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3335060/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3335060/https://www.tandfonline.com/doi/full/10.1080/21645515.2016.1177688?scroll=top&needAccess=trueoriginal here
https://www.lewrockwell.com/2021/07/no_author/covid-jab/ 