The Food and Drug Administration has authorized the use of booster shots of COVID-19 vaccines – another step taken by the U.S. towards providing extra shots to senior citizens and high-risk individuals.

Booster shots were signed off by the FDA for Americans aged 65 and up, and those who have existing health conditions and are at high risk of the virus due to employment situations.

But several regulatory hurdles are along the way before giving out the extra doses.

On Wednesday, the advisers to the Centers for Disease Control and Prevention convened to come up with their own recommendations on the target individuals eligible for the shot. With just the beginning of the meeting, there were already confusions from experts regarding the basis of the extra shots, making them suggest shelving the decision for some time to gather more evidence.

The qualms became an additional cue that the science around boosters is not as simple as what the current administration suggested last month when President Joe Biden and his leading assistants unveiled their plan.

Last week, the FDA’s panel of advisers turned down the president’s plan; thus, their Wednesday decision was expected. Boosters were only recommended by the panel to most at risk COVID-19 serious cases.

In a statement, FDA acting commissioner Dr. Janet Woodcock said that health care workers, teachers, those employed in grocery establishments, and people in prisons and homeless shelters are eligible for boosters, as authorized by the agency.

“As we learn more about the safety and effectiveness of COVID-19 vaccines, including the use of a booster dose, we will continue to evaluate the rapidly changing science and keep the public informed,” Woodcock said.

According to the authorization, vaccinated Americans can get the third dose after six months following their second dose of Pfizer vaccine, AP News reported.

“Today’s FDA decision is a major step forward in our effort to provide Americans with additional protection from COVID-19,” according to a tweet by White House press secretary Jen Psaki on Wednesday. “We have been preparing for weeks to administer booster shots to eligible Americans and are ready to do so following CDC’s final recommendation later this week.”