The Food and Drug Administration approved U.S. adults to get the COVID booster vaccine from Moderna and Pfizer on Friday. The decision comes weeks after scientists rejected the Biden administration's request to make them available on Sept. 20, citing a lack of data to support the need for a third dose.

The move also comes after data released earlier this month found that COVID vaccine efficacy wanes over time. A study showed that Pfizer went from being 86% to 43% effective, with Moderna falling from 89% to 58%, CNBC reports.

Prior to the decision by the FDA, White House chief medical advisor Dr. Anthony Fauci urged all adults 18 or older to get a third dose of the vaccine on Thursday. Speaking to MSNBC, he warned that "vaccine efficacy wanes over several months," while noting that Pfizer's shot is "still a very, very effective vaccine," The Hill reports.

Fauci pointed to studies released in Israel and the U.K. showing the booster shot dramatically increases protection against infection and hospitalization.

The Centers for Disease Control and Prevention is in charge of distributing the vaccines and will have to authorize the booster doses before people can start receiving their shots.

The move to distribute the additional vaccines comes at a time when case counts and hospitalizations are increasing around the country. Medical experts have debated whether or not the vaccine should be available for mass distribution in the states as the World Health Organization has argued it should be provided to underdeveloped countries first.

The WHO has said vaccinating those in the developing world prevents a new strain or another outbreak from emerging.

According to the CDC, 68.8% of Americans have received at least one dose of the shot and 58.9% of eligible people have been fully vaccinated.