The CDC is considering whether a third dose of the COVID-19 vaccine may help further protect immunocompromised people.
Health experts said the majority of breakthrough COVID-19 cases in fully vaccinated people typically are those who are immunocompromised.
Doctors on the CDC Advisory Committee said existing data suggests another dose could be helpful.
There was no final decision made on the issue Thursday, but some doctors on the committee said they need to act with urgency on this.
"Unfortunately, we're seeing more and more evidence that the immunocompromised groups, the specific ones, just don't get full protection from the COVID-19 vaccines," said Dr. Katelyn Jetelina, with UTHealth School of Public Health in Dallas
While the Pfizer and Moderna vaccines have shown to be about 95% effective in healthy people, doctors said that effectiveness can drop to as low as 20% for certain at-risk groups.
"This is especially true among organ transplant patients, among some cancer patients, and then even some people that are using certain immunosuppressive drugs. So unfortunately, they're just not protected," Jetelina explained.
Doctors with the CDC Advisory Committee noted France and Israel have already started to allow booster shots for those at high risk, and the UK, is currently considering it.
Blood cancer survivors and transplant recipients pleaded with the committee during public comment to approve a third shot now.
"A spike antibody test shows my antibody level at zero, completely undetectable. I know and you know that an additional shot might provide life-saving protection for people like me with little risk," kidney transplant recipient Robert Mnookin said.
Some doctors on the committee questioned how effective a third dose might actually be, while others said research shows a positive response.
"Among those who had no antibody response to an initial mRNA vaccine series, 33% to 50% did develop a detectable antibody response to an additional dose," Dr. Sara Oliver explained.
An FDA member at the meeting told the committee the agency is working as quickly as possible on options to allow a third dose.
But doctors are also concerned about time, with millions of vaccine doses set to expire over the next few months.
"This is running away with us. Time is of the essence. I appreciate how closely FDA is looking at the safety and how and how much research is being put into this decision. But I wish it would all happen faster," said Dr. Sandra Fryhofer, with the American Medical Association.
There has been no final decision on this issue yet.
The decision falls to the FDA and would then go to the CDC Advisory Committee for a possible recommendation.
There’s no exact timeline on when that might be.