There's less "stuff" in the mRNA vaccines than in any other. So for example, the fatal blood clotting conditions with the adenovirus-vectored vaccines turns ou

There's less "stuff" in the mRNA vaccines than in any other. So for example, the fatal blood clotting conditions with the adenovirus-vectored vaccines turns out to be due to the binding of PF4 onto the adenovirus capsid causing an autoimmune reaction to PF4 after it is "ingested" intracellularly. This doesn't happen with mRNA vaccines because there's no capsid or anything else. You're getting exactly the same mRNA payload with those, but you're wrapping it with a pile of other crap that you can have autoimmune reactions to. Similarly inactivated virus is not just the mRNA payload of the virus but all the rest of the viral machinery, surface proteins, nucleocapsid, etc. All of those get presented. Plus you probably need an additional adjuvant to stimulate your immune system. And the chemical makeup of the mRNA in the inactivated virus will trigger the innate immune system to kill the cells presenting it (the use of pseudouridine in the mRNA vaccines makes the mRNA look more host-like so that the cells don't get killed before presenting antigen on MHC). The risks of autoimmune conditions will stack based on how much more mRNA and proteins are present in the payload. There's a benefit of the inactivated virus in that you also get antibodies and T-cells to other proteins, including nucleocapsid, etc, but we just haven't seen any clinical net benefit after triple-vaccination (and if anything the outcomes of inactivated virus are slightly worse -- although after triple-vaccination HK studies have shown that they're comparable and that inactivated virus isn't particularly worse).