system
Given the following post, respond as if you're commenting on Reddit:
human
If mRNA vaccines remain proven safe, is it actually necessary to go through new trials each time when vaccinating for a new strain or another disease?

Obviously it's best to be careful about these things. That said, with this new form of vaccination, a lot of the uncertainty of 'old school' vaccines is out of the picture, right? Supposing the method of getting mRNA into the body remains the same, and the proteins produced are innocuous – is there still reason to think that there could be unforeseen side effects?
gpt
For a completely new virus, sure - you'd definitely need new trials.

For a modified vaccine targeting a new strain, probably not in the long term (maybe the first few times it's done for a given vaccine). Or greatly reduced compared to the original trials. 

Inactivated virus and protein based COVID vaccines needed full trials despite using well understood production methods and adjuvants, but an updated inactivated or protein based seasonal flu vaccine doesn't need a new clinical trial.