What makes boosters more effective than the first two Covid jabs?

Analysis: top-up vaccines make key changes to our antibody defences, reducing the threat from Omicron Coronavirus – latest updatesSee all our coronavirus coverageCovid-19, we should know by now, is a moving target. In autumn the rollout of boosters to older age groups was contentious. Now they’re the single biggest focus. So why do boosters help so significantly compared with first and second jabs, and are we on a conveyor belt towards needing an ever-increasing number of top-ups?Eve