I suggest your interpretation of such reasoning is questionable? I would posit any serious medical and or regulatory body is fully aware that an absolute statem

I suggest your interpretation of such reasoning is questionable? I would posit any serious medical and or regulatory body is fully aware that an absolute statement like "no known mechanism" resulting in complications isn't worth much in the face of highly complex and sometimes still little understood mammal bio-chemistry? What can be asserted with confidence though, is that in the presence of vaccines, severe effects of a infectious disease like COVID are significantly reduced - to the great benefit of the health system and society overall - and that, due to the quite different biological responses to vaccine vs. actual infection, severe effects in general are reduced massively. See lame-robot-hoax's comments. Nothing in life and certainly with regards to COVID is entirely risk free.