It's thought that the vaccines could remain effective long-term in the vast majority; this is currently being looked at, and antibody levels are still very high in most people 6 months to a year on from vaccination (this is using trial subjects). I think a booster campaign is being planned for the very vulnerable in a similar style to the flu jab campaign, however; the government wants to be safe rather than sorry in that regard. I think this will likely end up happening every year, with the vulnerable being called up for a COVID booster in the exact same way that they've always been called up for a flu booster each winter. Whether they stick to the top 4 priority groups as they always traditionally did with the flu vaccine or go more widely into the top 9 priority groups (as I believe they did with the flu jab in 2020, correct me if I'm wrong?) remains to be seen. In fact, didn't Nadhim Zahawi even say that the government has plans in place for a booster campaign to begin in September, come to think of it, with the top 4 priority groups (over-70s, healthcare workers and clinically extremely vulnerable) being targeted?