So you want magic. Got it.
In situations like the one five years ago, perfect understanding of how a new vaccine will interact with a relatively new virus is not going to be available.
Even more, perfect understanding of how good our information is at any given point in time is not always going to be available.
There were definitely some failures to communicate well with the public during that time, but demanding that only definite information be communicated, and then never be contradicted, is asking the impossible.
It also really doesn't help that there are so many people who were (and are) just so scared of everything during that time that any information coming out that wasn't 100% unquestionably positive about any new measure to try to improve things would cause them to shun it forever as too dangerous to try.