Top U.S. health officials have announced a plan to start offering Covid-19 booster shots to all Americans beginning in late September.

The offer for a third shot will be available to full vaccinated Americans, as Biden’s administration cited the threat from the highly contagious Delta variant.

With the announcement made on Wednesday, booster shots will be available for more than 155 million people who have been fully vaccinated with either the Pfizer or Moderna shots.

The booster shot would be given roughly eight months after receiving the second dose of the vaccine. The booster shots will be available beginning the week of Sept. 20.