A large part of the issue with understanding the risks of mRNA vaccines is that they have literally never been done before. On the other hand, some of the pote

A large part of the issue with understanding the risks of mRNA vaccines is that they have literally never been done before. On the other hand, some of the potential risks can be partially analyzed in terms of general principles. mRNA vaccines consist of messenger RNA combined with some form of carrier (vector) to allow it to enter cells (most cells do not normally let external RNA enter them). One in a cell, the mRNA will occasionally get picked up by a ribosome and used to make the protein it specifies. For mRNA viruses, this is usually a small portion of the viral shell that is distinct enough for the body to use to target the virus (antigen). mRNA has relative short half-lives inside cells on the order of a few minutes to a day or so. (Larger sequences appear to generally have shorter half lives.) Thus it is not considered likely that the mRNA itself will be able to have any long term negative effects, since it will fairly rapidly get broken down in the body. Once the mRNA is gone, the cells will cease producing the protein in question. Some Predictable Risks: 1. Unwanted effects of the carrier module. 2. the mRNA directly interacts with things in an undesirable way. (Either by binding to some other important RNA causing said other RNA to not function, or by the mRNA folding itself into some functional shape that harms things). 3. The resulting protein has some undesirable interactions with the body. 4. The resulting protein could misfold in a way such that it has undesirable interactions with the body. Even here, the effects are likely short term, although there exist ways it could become a long term effect. One theoretical way that could manifest is that it triggers misfolding in some unrelated protein into a prion configuration, thereby triggering a prion disease. 5. The normal risks associated with the activation of the bodies immune system. These are pretty much all possible with any vaccine, but specific attributes of a specific vaccine could make certain immune system risks more or less likely. 6. Other typical risks like contaminants in the vaccine. All told, I personally suspect that in general the risks from mRNA vaccines will be lower than live or deactivated virus vaccines, including the adenovirus vaccine approach of putting the +ssRNA for the antigen in an unrelated virus that has been made unable to replicate. But obviously the risks of any specific vaccine can vary versus other vaccines of the same basic type.