COVID-19 tests look for the coronavirus. And since none of the COVID-19 vaccines contain the coronavirus, they won’t cause you to test positive.
Getting vaccinated against COVID-19 can greatly reduce your chances of getting seriously ill if you do become infected. But if you test positive for COVID-19 after you’ve been vaccinated, it may be because you encountered the virus before your body had enough time to build up its defenses. It’s also possible that you were exposed to a variant of COVID-19 that is extremely contagious and can spread to people who are vaccinated.