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Moderately to severely immunocompromised people who received mRNA vaccines for COVID-19 should receive an additional dose, the CDC's Advisory Committee on Immunization Practices (ACIP) said on Friday.

In a unanimous 11-0 vote, the ACIP recommended an additional dose of the Pfizer (ages 12 and up) or Moderna vaccine (ages 18 and up) following a primary series in immunocompromised people, under the conditions of the FDA's emergency use authorization (EUA).

FDA authorized an additional dose for this population in amendments to the EUAs for the two companies' mRNA vaccines late on Thursday.

This additional dose should be the same type of vaccine as the mRNA primary series, though an alternate mRNA product can be used if there are supply issues. It should also be given at least 28 days after the primary series, CDC staff said in proposed clinical considerations documents.

In addition to solid-organ transplant recipients, CDC staff presented a potential list of other moderate to severe immunocompromising conditions that could qualify for an additional dose under the EUAs:

• Active treatment for solid-tumor and hematologic malignancies

• Receipt of chimeric antigen receptor (CAR) T-cell therapy or stem cell transplant (within 2 years of transplant or immunosuppression therapy)

• Moderate or severe primary immunodeficiency (e.g., DiGeorge, Wiskott-Aldrich syndromes)

• Advanced or untreated HIV infection

• Active treatment with high-dose corticosteroids (i.e., ≥20 mg prednisone or equivalent per day), alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, cancer chemotherapeutic agents classified as severely immunosuppressive, tumor necrosis factor (TNF) blockers, and other biologic agents that are immunosuppressive or immunomodulatory

Patients will self-attest if they have these conditions, and this will not require "medical sign-off" from any clinician or prescriber, CDC staff said.

ACIP Executive Secretary Amanda Cohn, MD, of the CDC, said that the intent of the EUA was to limit additional doses to individuals who were considered to have moderate to severe immunocompromising conditions, and that chronic health conditions, such as patients living in long-term care facilities or patients with diabetes or heart conditions, "is not the intent."

Indeed, the American Medical Association (AMA) stressed that this EUA was for a "limited population."

"Given that CDC data shows some immunocompromised patients lack the antibodies needed to fight COVID-19 infection, adding an additional dose to the primary series for this population can help protect these individuals from unnecessary hospitalizations and deaths," said AMA President Gerald Harmon, MD, in a statement.

CDC staff also warned against using serologic testing or cellular immune testing to guide clinical care, noting that no antibody tests are FDA-approved for the purpose of testing post-vaccination antibody levels.

Peter Marks, MD, PhD, director of the FDA's Center for Biologics Evaluation and Research, characterized the immunocompromised as a "heterogeneous group" in how they respond to COVID-19 vaccine, and cautioned that this additional dose could be "moderately effective at creating antibody titers."

However, CDC staff noted that these recommendations do not apply to immunocompromised individuals who received Johnson & Johnson as their primary vaccine, "due to insufficient data." CDC and FDA are currently engaged in additional research about this vaccine and expect to report back shortly.

"We had to do what we're doing with the data we had in hand," Marks said, adding that this is a solution for "a large majority of immunocompromised individuals" and that the agency hopes to "have a solution for the remainder in the not-too-distant future."

The Infectious Diseases Society of America (IDSA) applauded the ACIP's decision in a separate statement.

"While data on the use of a third dose of COVID-19 vaccine in immunocompromised patients is limited, there is sufficient data supporting its use for specific patient populations," said IDSA President-Elect Daniel McQuillen, MD. "IDSA calls for more research to continually inform optimal vaccination strategies for all immunocompromised patients."

In fact, CDC staff made the distinction between a third dose for immunocompromised patients and so-called "booster doses," meaning a dose for fully vaccinated patients when an initial sufficient immune response has waned over time.

For populations including residents of long-term care facilities, adults ages 65 and older, and healthcare providers, ACIP called for more data.

"Better correlates of immunity are sorely needed," said incoming ACIP Chair Grace Lee, MD, of Stanford University in California. She said it would be "really helpful to understand the gaps in the data currently existing" and urged a "strong partnership" between manufacturers, FDA, and NIH to "better define what correlates of immunity are."

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