FDA has authorized a second booster dose of COVID-19 vaccine for individuals who are immunocompromised or 50 and over.

The expanded emergency use authorization applies to the vaccines from Pfizer (NYSE: Pfizer) and Moderna (Nasdaq: MRNA).

Individuals interested in obtaining a second booster dose must wait at least four months after receiving the first booster dose.

Immunocompromised individuals should have an equivalent level of immunocompromise to solid organ transplant recipients.

Immunocompromised patients at least 12 can receive the Pfizer vaccine. Conversely, the Moderna vaccine is available to those 18 and up.

To make the decision, the FDA reviewed real-world data from Israel, which indicated that an additional dose provides added protection against SARS-CoV-2 without causing unexpected side effects.

The Israeli data are from an ongoing, open-label, non-randomized trial involving healthcare workers. Participants in the study who had received three total doses of the Pfizer-BioNTech COVID-19 vaccine received a second booster of either Pfizer-BioNTech or Moderna COVID-19 vaccine at least four months after the first booster shot.

The agency had previously authorized a single booster for some immunocompromised individuals who had received a three-dose primary vaccination series.

“Current evidence suggests some waning of protection over time against serious outcomes from COVID-19 in older and immunocompromised individuals,” said Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, in a statement.

FDA concluded that individuals facing a higher risk for severe disease, hospitalization and death from COVID-19 should be able to receive a second booster.

Pfizer shares ticked down 0.71% to $52.90 in early afternoon trading while Moderna shares were up 3.65%, hitting $179.41.