COVID AND THE VACCINE - TRUTH, LIES, AND MISCONCEPTIONS REVEALED, page-4391

Same as every other disease that's swept this planet that they've vaccinated for and over time in some cases even eradicated.

Because vaccinated peoples immune systems have been primed to recognise and attack the virus as soon as it enters the body they are less likely to build up the sort of viral load in their body that is easily transmitted to others.
Therefore the spread of the virus is slowed to the point it either dies out or becomes a background disease in the general population rather than a raging pandemic.