An advisory committee to the Centers for Disease Control and Prevention voted Friday to recommend that certain patients with weakened immune systems receive an extra dose of the Pfizer-BioNTech or Moderna vaccine.
The unanimous vote came less than 24 hours after the Food and Drug Administration amended the vaccines' emergency use authorization to include patients with moderate to severe immunosuppression.
The committee's recommendation will next go to CDC Director Dr. Rochelle Walensky, who must sign off on the committee's decision before physicians can start giving patients the extra dose. That could come as soon as this evening or over the weekend.
An estimated 2.7% of adults in the United States are immunocompromised, according to the CDC.
On Friday, the CDC's panel, called the Advisory Committee on Immunization Practices clarified who should be eligible for the additional shot. The group includes, but is not limited to, people who have received organ transplants, cancer patients undergoing treatment that compromises their immune system, as well as people with immunodeficiency syndromes, such as HIV.
Only patients who previously had one of the mRNA vaccines, from either Pfizer or Moderna, would qualify for a third shot. The CDC panel suggested that the third dose matches the vaccine previously administered.
That is, if a patient first received two doses of Pfizer vaccine, that person's third shot should also come from Pfizer. The same is true for Moderna. If that is not possible, however, the CDC committee said either mRNA vaccine would be appropriate.
Those who received the Johnson & Johnson COVID-19 vaccine, however, have been left out of this latest action.
The CDC committee said there is not yet enough data on immunocompromised patients who got the Johnson & Johnson shot to make any solid recommendation for an extra dose of vaccine.
It is unclear how many people fall under that category. Many immunocompromised patients got their vaccinations early on, before Johnson & Johnson was authorized, and therefore received an mRNA vaccine.
It remains unclear how much protection a third dose will provide to severely immunocompromised individuals. While studies are ongoing, ACIP member Dr. Helen Keipp Talbot, an infectious disease specialist at Vanderbilt University in Nashville, cautioned patients against assuming a third dose will fully protect them from COVID-19.
"I think the reality is, they'll be safer, but still at an incredibly high risk for severe disease and death," Talbot said. That is, immunosuppressed patients will still need to take extra precautions, such as continued masking and physical distancing.
This story originally appeared on NBCNews.com.