The Food and Drug Administration (FDA) has authorized individuals with weakened immune systems to get a third dose of the COVID-19 vaccine. 

The announcement came late on Thursday and applies to people with organ transplants, certain cancers, or other immunocompromising disorders. These individuals could get a booster from either Pfizer/BioNTech or Moderna, the FDA said. 

“Today’s action allows doctors to boost immunity in certain immunocompromised individuals who need extra protection from COVID-19,” Dr. Janet Woodcock, the FDA’s acting commissioner, said in a statement.

This highly anticipated measure taken by U.S. officials is a move to protect particularly vulnerable individuals, who make up about 3% of the U.S. population, as the nation sees a spike in COVID-19 cases due to the highly contagious Delta variant.  

It is harder for vaccines to strengthen an immune system suppressed by certain medications and diseases and those high-risk patients do not always get the same protection as otherwise healthy people. Small studies suggest an extra dose may be the solution, the AP reported.

The FDA reiterated that others fully vaccinated against COVID are “adequately protected” and currently do not need currently an extra dose, CNBC reported.

The Centers for Disease Control and Prevention is expected to meet Friday to discuss the booster shot for immunocompromised groups. If the third shot is approved, vaccines could start immediately.