In the UK at the moment there's some controversy regarding the changing of the timing of the Covid vaccination boosters.
All the vaccines I can think of that need boosters are given to babies, whose immune systems aren't fully developed yet. So they get some protection initially but need a booster when they're more mature. Are there any vaccines given to adults that actually need a booster? Was it used in the Covid trials for a good reason, or just to make doubly sure the results would be good? The information I can find online only covers the standard childhood vaccinations, and similar questions on this forum by other people over the past few years have remained unanswered.