By far the most widespread piece of misinformation still circulating is the "Vaccines do nothing to prevent infection" or "Vaccines have absolutely no effect in limiting transmission". I see it non-stop, always presented as a statement of fact, and often from people who are otherwise pro-vaccine.
If people genuinely believe this - and seemingly a big chunk of the population do - then it becomes much harder to make an argument to healthy people in their 20s, or similar, to get vaccinated.
Really needs a proper messaging campaign from the government/media.