No one has said the vaccines are 100% effective. Neither are natural antibodies.
The probability of so-called breakthrough infections (stupid term) doesn't seem to be known yet, but the current real-world data appear to indicate that the mRNA vaccines, at least—I haven't seen real-world data regarding any of the others—are quite effective for the overwhelming majority of individuals.
Most people who are exposed to someone who is shedding the coronavirus and have been "fully vaccinated" with either the Moderna or Pfizer/BioNTech product (two doses plus a two-week waiting period) won't get infected at all. Of those who do get infected, approximately 10 percent or thereabouts, only about half will get sick. Of those who get sick, few will need hospitalization. A very small number will die.
In the meantime, if you aren't exposed to the coronavirus, you can't get infected. Period. Full stop.
So until you have been vaccinated, if you want to avoid getting sick, don't spend any more time than necessary indoors with strangers; wear an effective facemask* when you must spend time indoors with people other than those in your household and, while you're doing that, maintain as much distance as possible from them; wash your hands after touching smooth surfaces which have been recently handled by strangers. These are the same simple and easy-to-observe precautions that have been understood for many months now by anyone paying attention.
After you have been vaccinated, keep doing these things because some vaccinated or previously-infected individuals are expected to become infected if they come into contact with someone who is shedding the virus. These are the "breakthrough" infections. And, of course, you could become infected, yourself, not have symptoms or not have them yet, and transmit the virus to other people.
If you
have been vaccinated and you really want to spend time indoors with people other than those in your household without observing these precautions, verify that they have also been vaccinated and that the venue where you intend to meet will not expose you to other individuals who are unvaccinated or whose vaccination status you can't verify.
Of course, if everybody took these precautions, the reproduction factor of the virus would quickly fall below 1.0, the frequency of new cases would be reduced dramatically, and the risk of coming into contact with an infected individual soon would become low enough that none of these precautions would be necessary any longer.
In other words, once there is little or no chance you will be exposed to the virus, you won't get infected. Period. Full stop.
Alternately, you are within your rights (at least in most industrial democracies) to ignore the precautions, take your chances, and be confident that you are doing your part to retard the return to normal life.
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E.g., an N95, KN95, or FFP2 respirator, properly fitted, or a surgical mask covered with a tight-fitting cloth mask to pull the edges of the surgical mask close to your face.
