When people say, for example, "the vaccine is 80% protective against severe disease", does that mean: (A) if you've had the vaccine, your likelihood of severe covid (if you get infected) is 20% Or (B) your likelihood of severe covid (if you get infected) is 20% of whatever it would have been if you were unvaccinated (This is just an example statistic, I'm aware that it's more complicated in terms of different types of vaccine and different strains of covid and number of doses of vaccine)
It ought to be B. If you were going to get severe disease the vaccine stops that for 80% of people. So if your chance of severe diseases was 23% without vaccine it would be 4.6% after the vaccine.
I did a stats module at uni but I am RUSTY haha! Plus never sure whether I can assume that the media are communicating statistics accurately.
