It appears that Pfizer failed to test the vaccines for obvious safety issues:
"The Pfizer records include a report, which was approved in February 2021, on the animal trials on the distribution of the Pfizer COVID vaccine in rat subjects, in a section titled “Safety Pharmacology,” the report notes, “No safety pharmacology studies were conducted with BNT162b2 [the BioNTech vaccine] as they are not considered necessary for the development of vaccines according to the WHO guideline (WHO, 2005).” Similarly, under “Pharmacodynamic Drug Interactions,” is “Nonclinical studies evaluating pharmacodynamic drug interactions with BNT162b2 were not conducted as they are generally not considered necessary to support development and licensure of vaccine products for infectious diseases (WHO, 2005).”
...
"This same Pfizer/BioNTech study notes “No genotoxicity studies are planned for BNT162b2 [the Pfizer/BioNTech COVID vaccine] as the components of the vaccine constructs are lipids and RNA and are not expected to have genotoxic potential (WHO, 2005).” Similarly, “Carcinogenicity studies with BNT162b2 have not been conducted "

In spite of all this evidence that Pfizer did not take steps to insure safety the CDC, FDA, and WHO ignored their duties and approved the untested, experimental (and now shown to be harmful) vaccines.