If they were detected as unsafe during testing they wouldn't be available. That's the point. You only know of vaccines that passed the tests, not those that didn't.

> “Vaccines” have such good standing because the general idea of improving immunity by exposing the immune system to non-infectious material that closely matches some part of the infectious agent works really well. There’s not much room for things to go wrong unless the material actually turns out to be infectious, as was the case with the dangerous vaccine I mentioned above.

Infectiousness is not the only risk. Look at polio vaccines causing polio.

…what