Without a delineation, how do you argue that it is effective? How how do you argue that any treatment is effective if not statistics like these? And it’s not fair to say no vaccine survives this delineation because I specifically used Polio as an example of an effective vaccine.
There isn't a magical number which means the vaccine is effective, and below that number it is ineffective. A vaccine is effective if it helps people deal with a virus (i.e. lowering chance of hospitalisation/death). It doesn't magically become ineffective because it doesn't meet an arbitrary percentage of prevented cases.
The Polio vaccine is "only" 99-100% effective. That means that it's not 100% effective (as in, there are cases where it doesn't prevent transmission/infection). According to the criterium laid out by GP this means it is an ineffective vaccine, just like the Covid vaccine.
