The U.S. Food and Drug Administration (FDA) on Thursday authorized a third dose of COVID-19 vaccines for people with weakened immune systems.

"The country has entered yet another wave of the COVID-19 pandemic, and the FDA is especially cognizant that immunocompromised people are particularly at risk for severe disease," Acting FDA Commissioner Janet Woodcock said in a statement.

"After a thorough review of the available data, the FDA determined that this small, vulnerable group may benefit from a third dose of the Pfizer-BioNTech or Moderna Vaccines," Woodcock added.

"The FDA is actively engaged in a science-based, rigorous process with our federal partners to consider whether an additional dose may be needed in the future," Woodcock said.

An estimated 2.7 percent of adults in the United States are immunocompromised, according to the Centers for Disease Control and Prevention. That includes organ transplant recipients, certain cancer patients and people with HIV.