As we head into what might – or might not – be a perilous winter, it would be nice to have the answer to some vaccine questions: depending on how long ago you had yours, how protected against Covid-19 are you right now? Has your vaccine waned in its effectiveness? What if you had Covid at some point this year? Are you better off having had one brand of vaccine versus another? And how much do you need a booster shot?
These are difficult questions to answer. As case numbers go up and down, as people’s behaviour changes, and as natural immunity levels rise, it becomes increasingly messy to draw conclusions. Different groups of people were offered different vaccines as the rollout went on, adding a potential confounder into any analysis. And let’s not forget the different variants: studies have to ask whether any decline in protection is due to the vaccine actually waning, or the older virus being replaced with the more dangerous Delta variant (in that case, the waning presumably wouldn’t continue if no new variants of concern appear).
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