That's why you might get infected with COVID-19 even after the vaccine

This happens for several reasons:

Immunity is not won immediately: It takes time for vaccines to create immunity. People can be exposed to the coronary before they are vaccinated, or right behind it, and thus there is no time for the body to develop its defenses.

Vaccines may not offer perfect protection from coronary: Both vaccines provided 95% protection in clinical trials.

This means that a 5% of people can become infected again after taking two doses of the vaccine.

Immunity may fade over time: Nobody knows how long it will protect vaccines from infection.

There is also the possibility that the new coronary will create mutations in a way that makes vaccines less effective.