I'm not specifically an mRNA vaccine expert, but I have a biomedical science PhD, and my "generally well educated in this area" gut feeling is that mRNA vaccines are a simple, "clean" formulation with less chances for something surprising to go wrong compared to other vaccine formulations.
I got the Moderna shot and I've been totally nerding out about how cool it is. It's just mRNA, which basically falls apart when you look at it funny, with just enough lipids to hold it together until it gets into your cells. If there were going to be terrible side-effects, I would expect them to show up immediately or not at all, since the constituent ingredients are simple things that break down quickly in the body.
I got the Moderna shot and I've been totally nerding out about how cool it is. It's just mRNA, which basically falls apart when you look at it funny, with just enough lipids to hold it together until it gets into your cells. If there were going to be terrible side-effects, I would expect them to show up immediately or not at all, since the constituent ingredients are simple things that break down quickly in the body.