it's related to the time in care between the first visit following an event and the last visit pertaining to that same event. as in the total number of days between and not the number of visits between, in which case it's protective relative to listing total visits. like in the case that 2 people with the same negative event might come a couple of times vs every day until it abates
What about the case where one group (hypothetically the unvaccinated) simply doesn't seek healthcare for as many things? Is it assumed that if two people have the same DOC then they're both equally likely to visit the clinic for the same symptoms?