That’s not how vaccine effectiveness works. There’s already a probability less than one of getting Covid if unvaccinated, and the effectiveness of the vaccine is the reduction from that.

So if over the course of their study period, 100 unvaccinated people got covid out of a thousand tracked, with a 98% effectiveness, only 2 people in the 1000 people vaccinated group would have gotten it.

So vaccines are really effective. Even more so for preventing serious complications.