The FDA just authorized booster shots of Pfizer's and Moderna's COVID-19 vaccines for all adults

• All adults in the US are now eligible to get a booster shot.
• The FDA on Friday expanded its emergency OKs for the Pfizer-BioNTech and Moderna COVID-19 shots.

The Food and Drug Administration on Friday expanded its emergency authorizations for booster shots of the Pfizer-BioNTech and Moderna coronavirus vaccines, making all adults in the US now eligible for an additional shot.

The US regulator previously authorized booster shots for older and higher-risk populations. Friday's announcement expands and simplifies the US booster-shot campaign, which has been mired by confusion over when, and whether, people need another dose.

"Authorizing the use of a single booster dose of either the Moderna or Pfizer-BioNTech COVID-19 vaccine for individuals 18 years of age and older helps to provide continued protection against COVID-19, including the serious consequences that can occur, such as hospitalization and death," Dr. Janet Woodcock, acting commissioner of the FDA, said in a statement.

So far, 71% of adults in the US are considered fully vaccinated, meaning they've received two shots of the Pfizer-BioNTech or Moderna vaccine or received the single-dose Johnson & Johnson vaccine. About 31 million Americans have also received a booster dose, according to the Centers for Disease Control and Prevention.

National guidelines from the CDC had already allowed adults to get a booster shot if they were 65 or older, if they were living in long-term care settings, or if they had underlying health conditions or worked in areas with high risk of exposure. Three states — Colorado, California and New Mexico — as well as New York City had already bypassed these guidelines and were allowing all adults to get booster shots.

The CDC's advisory committee is scheduled to meet Friday to review and discuss its own booster-shot recommendations, incorporating this latest FDA authorization.

Adults who got the Moderna or Pfizer-BioNTech vaccine are eligible for a booster shot six months after their second dose. J&J recipients can get a booster shot as soon as two months after their initial vaccination. Children and teenagers are still ineligible to receive booster shots.

The FDA previously allowed people to mix-and-match vaccine brands for a booster shot, meaning recipients of the Moderna or J&J vaccines could get the Pfizer-BioNTech booster shot.

Moderna applied on Wednesday to expand its booster shot to cover everyone 18 years and older.

Government leaders and public-health officials have recently expressed concern about the winter season and the threat of another surge in infections and deaths. Dr. Anthony Fauci, the director of the National Institutes of Health's infectious-disease division, told Insider's Hilary Brueck that the extra dose was a valuable tool in preventing illness and that all adults should get boosted.

"The effect of boost is very, very favorable to preventing people from getting infected," he said.