LOS ANGELES - The US Food and Drug Administration (FDA) on Tuesday authorized a second booster dose of either the Pfizer-BioNTech or the Moderna COVID-19 vaccines for older people and certain immunocompromised individuals.

A second booster dose of the Pfizer-BioNTech COVID-19 vaccine or Moderna COVID-19 vaccine may be administered to individuals 50 years of age and older at least 4 months after receipt of a first booster dose of any authorized or approved COVID-19 vaccine, said the FDA.

Meanwhile, the FDA authorized a second booster dose of the Pfizer-BioNTech COVID-19 vaccine to be administered to individuals 12 years of age and older with certain kinds of immunocompromise at least 4 months after receiving a first booster dose, and a second booster dose of the Moderna COVID-19 vaccine be administered to individuals 18 years of age and older with the same certain kinds of immunocompromise.

The FDA has determined that the known and potential benefits of a second COVID-19 vaccine booster dose with either of these vaccines outweigh their known and potential risks in these populations.

"Emerging evidence suggests that a second booster dose of an mRNA COVID-19 vaccine improves protection against severe COVID-19 and is not associated with new safety concerns," said the agency in a statement.

The FDA previously authorized a single booster dose for certain immunocompromised individuals following completion of a three-dose primary vaccination series. The new move has extended the availability of a second booster dose to other populations at higher risk for severe disease, hospitalization and death.

"Current evidence suggests some waning of protection over time against serious outcomes from COVID-19 in older and immunocompromised individuals. Based on an analysis of emerging data, a second booster dose of either the Pfizer-BioNTech or Moderna COVID-19 vaccine could help increase protection levels for these higher-risk individuals," said Peter Marks, director of the FDA's Center for Biologics Evaluation and Research.

"Additionally, the data show that an initial booster dose is critical in helping to protect all adults from the potentially severe outcomes of COVID-19. So, those who have not received their initial booster dose are strongly encouraged to do so," he said.

The second booster for adults 50 and older and for people 12 and older who are immunocompromised is expected to become available immediately after the US Centers for Disease Control and Prevention reaches a decision on who should get it.