"Before approval by the Food and Drug Administration (FDA), vaccines
are evaluated for efficacy and safety using large Phase III randomized controlled trials. For childhood vaccines, the number of children enrolled in
these trials is typically in the thousands. That is sufficient to detect common
but not rare adverse events."

And they've told us "it's safe! to trust them!" yet, they have NO EVIDENCE of that safety and they admit it here.

Very few postmarketing studies
have evaluated whether the risk of adverse events depends on the scheduling of the vaccines. For example, few postmarketing studies have evaluated
whether the risk of adverse events depends on the age at which a vaccine
is given, on the relative timing of two different vaccines, or on a combined
cumulative effect generated by the timing of dozens of different vaccines.

These are all different components of the vaccine schedule, and any one
of these could potentially be related to the number and severity of adverse
events. When evaluating the safety of different vaccine schedules, it is hence
important to study the whole range of issues, from the timing of a single
vaccine to summary metrics based on the timing of dozens of vaccines"

https://www.ncbi.nlm.nih.gov/books/NBK206948/pdf/Bookshelf_NBK206948.pdf