I'm sure it's rare, but when it does happen it makes waves. The chinese lab leak theory is the first thing that comes to mind, but also the CDC director going on TV to tell the nation if you got vaccinated you wouldn't catch covid, get sick, or spread covid is another that comes to mind.
Vaccination rates in children have plummeted, and I suspect if we thought anti-vax rhetoric was bad pre-covid, it's not going to hold a candle to the near future.
A big complication when judging things like this is that, like many relationships in political/social dynamics, there is strong asymmetry. Similar to the saying that a black American must be twice as good a citizen to be considered half as good a citizen (i.e. flaws/failures are counted more heavily against them), tons of people can espouse harmful/baseless theories all day, and they will receive criticism and support that doesn't really add up to anything unusual, but when one person who said "that's not true" turns out to be wrong, it "makes waves", as you say. This makes sense, since, on the theorists' side of things, they feel like the underdogs and the nay-sayers feel like the elites; and on the nay-sayer's side of things, they are typically being held to a higher standard by even their fellows. In other words, the optics/feelings don't really match up with pragmatic/generous observation.
Another problem, which I think is more overlooked, is that when people talk about the cases of the nay-sayers being wrong, it frequently goes like this:
- Theorist claims uncomfortable truth X.
- Nay-sayer says X is not true.
- X turns out to be true.
However, most of these cases are really closer to something like this:
- Theorist claims X, which, if untrue, is a harmful thing to spread.
- Nay-sayer says there is no (or not enough) evidence for X (which is way different from insisting that X is not true).
- X turns out to be potentially true, partially true, or true for a specific case (and sometimes unqualifiedly true!).
In reality, there are vanishingly few of the former case, and even for those cases that exist, the nay-sayer's case is still frequently the better case and could reasonably be held again if the same scenario happens again, where the theorist's truth is arguably a broken-clock scenario.
If the CDC director made a false statement about what a vaccine can achieve (i.e. milder or less symptoms), then that's a bad mistake, but it's not "a top expert claiming something is a CT but later it turns out it wasn't".
When you have people claiming the vaccine doesn't work and a public figure goes to the press to overstate that the vaccine not only works, but it is essentially, perfect, then it's not a bad mistake - it's a knee-jerk response to the "conspiracy" criticism without evidence.
Sure, pundits on 24h news are often wrong, but I wouldn't call them top experts, more like hot-take-deliverers. Believe them at your peril.