A key CDC advisory panel presented evidence that an additional shot could boost the chances that people with weakened immune systems will get a protective response. Right now, such use isn't allowed.

Transcript

LULU GARCIA-NAVARRO, HOST:

Booster shots or not? Federal health advisers are debating whether some people, especially those with weakened immune systems, need a third dose of the COVID-19 vaccine. NPR's Maria Godoy has more.

MARIA GODOY, BYLINE: First, let's be clear. If you're a fully vaccinated person with a healthy immune system, the evidence suggests you're still well-protected against severe disease and hospitalization from COVID-19. However, that's not always the case for people who are severely immunocompromised - for instance, because they've got cancer, take powerful immunosuppressive medications or are organ transplant recipients. This population can fail to mount a strong defense against the coronavirus, even after two doses of the Pfizer or Moderna vaccines.

This week, an important federal advisory committee at the Centers for Disease Control and Prevention presented data suggesting that a third dose of vaccine could significantly boost the chances that a person with a weakened immune system will have a protective response. For example, recent studies found that among patients who produced no antibodies after two shots, as many as half of them developed antibodies after an additional shot. Dr. Grace Lee is a professor of pediatrics at Stanford and a member of the CDC's Advisory Committee on Immunization Practices.

GRACE LEE: You know, I think that there is sufficient data to suggest that an additional dose would be helpful.

GARCIA-NAVARRO: Lee and others on the panel said they'd like to see safety monitoring of people who get third shots, although studies so far suggest they're unlikely to pose a risk. Health officials in France and Israel are already giving third doses of vaccine to people with severely compromised immune systems. But here in the U.S., regulators are still reviewing data, and they have yet to authorize an additional dose of any vaccine. Until they do, doctors aren't allowed to recommend a third dose. Dr. Camille Kotton is a transplant specialist at Massachusetts General Hospital. As she noted to her fellow panel members, some immunocompromised patients are already getting an additional dose on their own.

CAMILLE KOTTON: I am concerned about them doing this kind of in an unsupervised fashion. But as it is right now, due to regulatory issues, we are not allowed to recommend additional doses. So patients are really just doing with what they think is best.

GODOY: A CDC vaccine official said the agency is exploring ways it might be able to get third doses to immunocompromised patients, potentially through a clinical study, for example, even before regulators change the rules. Maria Godoy, NPR News. Transcript provided by NPR, Copyright NPR.