And the very bad news is that it may be possible to create a bioweapon that targets only people with a specific spike protein.
The mRNA "infects" the host cells and starts generating spike protein. The desired result is IgM/IgG titer against spike protein. The intended alternatives include the "toll like" response where spike protein expressed on a host cell is treated as "self" by the immune system and no defense is mounted. Viremia has been observed with that response. Another option is the IgG is created and attacks the host cells generating the spike protein. The mRNA is non-specific about what it "infects", so you have the immune system attacking the host cells on exposure to a "wild type" SARS-CoV-2 virus that triggers a response. Kills the virus and the host. Oops. This latter situation was observed in mouse studies MONTHS after the vaccine was administered. We're just jabbing now, so it may be months before this effect is observable. All the mice died.