Battle for Boosters: A Third Dose for the Immunocompromised

Sandra Adamson Fryhofer, MD


October 01, 2021

This transcript has been edited for clarity.

This is part 1 of a Medicine Matters series on "Battle for Boosters." This segment addresses additional vaccine doses for immunocompromised people.

Immunocompromised persons were not included in the phase 3 trials of COVID vaccines. COVID vaccines don't work as well in immunocompromised people. Immunocompromised patients are more likely to have breakthrough infections. Studies show that 40%-44% of hospitalized breakthrough cases are in immunocompromised people. Vaccine effectiveness ranges from 59% to 71% in immunocompromised patients as compared with 90%-94% effectiveness in patients who are not immunocompromised.

Immunocompromised people make up about 2.7% of all US adults (about 7 million people). They are more likely to transmit COVID to people they live with as well as other household contacts. Immunocompromised patients are also more susceptible to infection with COVID variants. They are also more likely to stay sick with COVID longer. Prolonged infection gives the virus more time to evolve and mutate and transform into new variants.

On August 12, 2021, the FDA authorized an additional COVID vaccine dose for certain immunocompromised people. This extra dose gives these vaccinated but still vulnerable patients a greater chance of making enough antibodies to protect them from COVID.

CDC has posted detailed guidance on specifics of who qualifies as immunocompromised. For immunocompromised patients, in order to get the additional dose, no prescription is needed. A doctor's note is not required. There is no need to check for COVID antibodies. Antibody testing before giving the additional dose is not recommended. Antibody testing post vaccination is also not recommended.

The type of vaccine the patient initially received matters. Mixing and matching mRNA vaccines is not preferred but is allowed. For immunocompromised persons, ACIP recommends an additional dose of either Pfizer (for those 12 and older) or Moderna (for those 18 and older) following a primary mRNA vaccine series. Give the additional dose at least 1 month after the primary series. Try to give the same type of additional dose as the original series if you can.

The recommendation only applies to those who got Pfizer or Moderna vaccines. It does not apply to those who received a single dose of Janssen's viral vector vaccine. That said, because the Janssen vaccine was authorized much later, the number of immunocompromised patients who may have received it is probably small.

An additional vaccine dose for immunocompromised patients is not a booster. This additional dose is part of an augmented primary series when the regular primary series was not protective. A booster is given when protection begins to wane over time.

But even with this third dose, protection is not guaranteed. Immunocompromised patients still need to follow prevention measures: Wear a mask, practice social distancing, and avoid crowds and poorly ventilated indoor spaces. And, of course, all close contacts should be fully vaccinated.

Follow Medscape on Facebook, Twitter, Instagram, and YouTube


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.
Post as: