> I imagine the cancer vaccine trial wasn't successful, as the current mRNA vaccines are indeed the first to enter public use

Yeah, but you see how non-reassuring it is. :P

I do find it reassuring because it implies we have data from that trial and others going back over a number of years.

I imagine it didn't proceed as the treatment wasn't effective, rather than because everybody died from the vaccine. And if there were problems with the vaccine itself, then I would think that knowledge would feed into the design/implementation of future iterations of mRNA vaccines.

So yeah, that's what I take from that. I find the existence of a decade of trials of the tech, and the approval of these two vaccines after a bunch of their own trials, and the ongoing monitoring of outcomes, to be fairly reassuring.

That said, I got the AZ vaccine, because that's what I was offered!

> the approval of these two vaccines after a bunch of their own trials

Which two? If it is still the case, Pfizer and Moderna were not approved at all by the FDA. They were given emergency use authorization only by the agency. As I said before, the whole approval process takes years, unless they are authorized for emergency use, as it is the case with COVID-19 vaccines.

You have to realize that they did not have their own "bunch" of trials. It would have taken years to properly go through the process. We are studying them now, some time passed since first vaccinations, hence why there is emerging information about side-effects.

They've been given emergency approval, sure.

> You have to realize that they did not have their own "bunch" of trials.

Yes, they did. Sorry but this is where you veer into outright misinformation. There have been trials ongoing for a while. The specific two mrna vaccines you are concerned about have had trials, with phase 1/2 reporting last summer and phase 3 interim reporting starting late last year. Your own link above puts these at the end of the process, and your other link says development can take years, not that it must or always does.

Are all trials complete? No, they aren't. But to state they haven't had trials is incorrect.

So in summary -

The tech has been studied for 30 years.

Human vaccine trials using it started 10 years ago.

Trials have taken place and have reported, though phase 3 is ongoing and will continue to report (this is not the same as it not happening, there has already been useful clinical data).

We now also have several months of data from worldwide rollout, with multi-hundred-million doses administered, all of which is continuing to make these things look incredibly safe.

That's not enough for you? Do you need some sort of an absolute guarantee of safety handed down by god himself, amidst a raging pandemic?

There's no reason to think that there should be long term health consequences to these. We have lots of data saying short/mid term consequences are rare and mostly very mild, we have a fair body of data going back ten years which leads us to expect that mRNA vaccines are not long term dangerous as a category (or they would not be given their emergency authorisation)... at this point I think the judgement needs to be that any long term consequences that might appear are far less likely to be a problem than covid itself, yes, even for those age groups affected by pericarditis/myocarditis.