Why does Covid-19 vaccine protection wane?

Covid is surging across Europe, but what's causing it, and will the UK follow suit, or are Europe hot on our heels? Should vaccines be mandatory, and would vaccine passports work? Why does Covid-19 vaccine protection wane with time, and are we looking at a relentless cycle of boosters indefinitely, or will one be sufficient? Dr Chris Smith joins RNZ's Kim Hill for a catch-up all about the current state of Covid-19... Like this podcast? Please help us by supporting the Naked Scientists