The Food and Drug Administration is poised to amend the emergency use authorizations for the Pfizer and Moderna COVID-19 vaccines Thursday to allow people with compromised immune systems to get a third dose, according to two sources familiar with the plans.
The move would come after a panel of advisors to the Centers for Disease Control and Prevention met in July and urged action on extra doses for immunocompromised adults.
Doctors say it is increasingly clear that many such patients are still vulnerable to COVID-19 following vaccination because they may not mount an effective immune response to the shots.
An estimated 2.7% of adults in the United States are immune-compromised, according to the CDC. It is unclear which groups would be covered under the expected FDA action. Immune-compromised patients include organ transplant recipients, people undergoing cancer treatment and people with HIV, among others.
Organ transplant recipients, for example, must take medications to suppress their immune systems so their bodies do not reject the new organs. One small study of these patients found the majority never developed antibodies to the coronavirus after vaccination. The others only developed low levels of protection.
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In that study, from Johns Hopkins University, a third dose increased their antibody levels.
A boost in immunity would likely be welcome to those who never had a good response from the first two shots, as doctors have continued to advise such patients to continue with physical distancing and masking despite the vaccines.
The emergency use authorization does not include fully vaccinated, otherwise healthy people for which both the Pfizer and Moderna vaccines have been shown to be highly effective at preventing hospitalization and death.
The CDC advisory group is scheduled to meet Friday, where they may vote on whether to officially recommend a third shot for immune-compromised people. The panel’s sign off is needed before doctors could start prescribing extra doses.
Such a vote is only done after the FDA takes regulatory action, such as the expected amendment to the emergency use authorization.
Last week, the Mississippi Department of Health recommended immune-compromised people receive an additional vaccine dose, despite the fact that federal health officials had not yet signed off on it.
This story first appeared on NBCNews.com.