The FDA requires vaccine manufacturers to include specific items on their package inserts, including information about reported adverse events following vaccine administration.
“Adverse reactions. This section must describe the overall adverse reaction profile of the drug based on the entire safety database. For purposes of prescription drug labeling, an adverse reaction is an undesirable effect, reasonably associated with use of a drug, that may occur as part of the pharmacological action of the drug or may be unpredictable in its occurrence. This definition does not include all adverse events observed during use of a drug, only those adverse events for which there is some basis to believe there is a causal relationship between the drug and the occurrence of the adverse event.”
But the FDA does not require manufacturers to do anything about these adverse events, other than report them. Between the lack of responsibility of vaccine makers, the lack of an adequate vaccine adverse event surveillance system, and the lack of any inert placebo studies of vaccine products, the number, type, and magnitude of risks are simply not known — and this is intentional.