What? They have been studied. For this and for other vaccinations. Kids get duplicate MMRs all the time because of lost paperwork.

Sometimes it feels like a new virus comes along and people forget we have 111 years experience with vaccinations.

It's not even the same technology.

But the method is identical. Get cells to present the proteins you want blasted. One uses direct mRNA deposition, the other hoodwinks denatured viruses into doing exactly the same thing.

mRNA isn't a scary new thing, it's a fundamental part of cell function. The clever new thing here is that we can bung it directly into cells to make proteins without having to mess around with carrier viruses.

Hundreds of millions of people have been exposed to covid and have also had a vaccine now, so even forgetting that there's no theoretical problem here, it has a physically tested track record.