Thanks for your well-reasoned comment. I assume by "odds ratio minus one", you mean odds ratio of 2 is 100% and odds ratio of 1 is 0%? Because 2-1 = 1 and 1-1 = 0 (thus 100% and 0%). If so, 100% increase is still a 2-times.

So that would mean, in your example, the virus is twice as bad as the vaccine in increasing POTS risk. But in this case, the vaccine is equivalent to control since it doesn't increase POTS risk. So, it's rather misleading to say the virus is twice as bad as the vaccine, because it implies the vaccine is bad to some extent? Then maybe we could say POTS risk remains unchanged from vaccination but doubles from infection?