A Third Dose of the COVID-19 Vaccine Recommended for Some Cancer Patients With Weakened Immune Systems: Latest Information

Patient receives a COVID-19 vaccine

Some people with cancer may need to receive a third dose of the COVID-19 vaccine.

As you may have heard, the Centers for Disease Control and Prevention (CDC) has recommended a third dose of the COVID-19 vaccine for people who are immunocompromised. This includes some — but not all — people with cancer.

Mini Kamboj

Mini Kamboj

Mini Kamboj, Memorial Sloan Kettering Cancer Center’s Chief Medical Epidemiologist, has answers to your questions about who is eligible and how you can schedule an appointment to receive your third shot.

Why do immunocompromised people need a third dose of the COVID-19 vaccine?

For a vaccine to protect you, it must activate your immune system. In some immunocompromised patients, this ability is impaired, so a third dose can boost the immune response.

According to the CDC, among severely immunocompromised people who had undergone solid organ transplant and had virtually no protection after receiving two doses of the Pfizer-BioNTech COVID-19 vaccine (Comirnaty®) or Moderna COVID-19 vaccine, 30 to 50% developed antibodies protecting them from COVID-19 after getting an additional dose.

MSK researchers have found that the COVID-19 vaccines may not be as effective in people with certain blood cancers. A study led by medical oncologist David Chung found that people with blood cancers have a weakened antibody response to the vaccines, both due to the cancer itself and because of treatments for the disease. Another study, led by Roni Tamari and Gunjan Shah, found that people who had received bone marrow transplants or other cellular therapies for their cancer within the previous year also got less protection from the vaccines.   

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Who is eligible for a third dose of a COVID-19 vaccine?

People who have moderate to severe immunosuppression qualify to receive an additional dose, usually because of an organ or stem cell transplant, HIV infection, steroid therapy, or certain cancer treatments that impair the body’s ability to fight infections.

It’s important to know that not all cancer patients have a weakened immune system. Those cancer patients who are considered immunocompromised include:

  • Patients being treated for blood cancers currently or within the last six months
  • Patients who were within 12 months after treatment with B-cell depleting drugs (for example, rituximab or Rituxan®) at the time of their initial vaccination
  • Patients who have undergone a stem cell transplant or received CAR T therapy within the last two years
  • Patients being treated for solid tumors with chemotherapy — and some patients on immunotherapy — currently or within the last six months

These eligibility criteria cover the most common indications. Your provider will be able to order the third vaccine dose for other immunosuppressive treatments or conditions if they decide that the extra dose will benefit you. 

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Which cancer patients are not eligible for a third dose at this time?

  • Patients with solid tumors are not considered immunocompromised if their cancer has been treated with hormone therapy, targeted therapy, surgery, radiation, or is under observation only.
  • To ensure the best immune response to the third dose, MSK experts recommend that certain patients discuss the optimal timing of the extra dose with their clinical care team. This includes recent treatment involving stem cell transplant, CAR T treatment, or anti-CD20 monoclonal antibodies.
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When should eligible patients get a third dose?

If you meet the criteria, you can receive a third dose 28 days or later after completing your first vaccine series.

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Which vaccines can be used for a third dose?

Only patients who completed their primary immunization with either Pfizer-BioNTech or Moderna vaccines can receive the third dose. MSK will offer the same vaccine brand to patients as they previously received. Mixing vaccines is not permitted at this time.

The CDC has not made any recommendations yet for people who received the Johnson & Johnson vaccine. We are closely following their guidance and will communicate any changes.

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How do I make an appointment?

To find out if you should get a third dose, call your MSK doctor’s office or send a message through the MyMSK patient portal. If you are eligible for an additional vaccine, your doctor will schedule an appointment for you.

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When and where will MSK begin administering third doses?

On Wednesday, August 18, MSK will begin offering the additional vaccines at the David H. Koch Center for Cancer Care at Memorial Sloan Kettering Cancer Center, located at 530 East 74th Street.

Starting Monday, August 23, we will be scheduling appointments at:

  • MSK Westchester, located at 500 Westchester Avenue in West Harrison, New York
  • MSK Nassau, located at 1101 Hempstead Turnpike in Uniondale, New York

These clinics will be open 9:00 a.m. to 5:00 p.m., Monday through Friday.

Additional dates and locations, including our New Jersey locations, will be added shortly.

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I’m an MSK patient who was vaccinated outside of MSK. What should I do? 

If you think you meet the criteria for getting a third vaccine dose, you should call your provider’s office to confirm your eligibility, and a vaccine appointment will be scheduled for you. You should be prepared to share your vaccination card or a photo of it. Please present information from your card, rather than the Excelsior pass, which does not have the details about what vaccine brand you received and on what dates.

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Are pediatric patients with weakened immune systems eligible to receive the third vaccine dose?

Yes, the Food and Drug Administration (FDA) has granted emergency use authorization for patients 12 and older to receive the Pfizer-BioNTech vaccine and 18 and older to receive the Moderna vaccine.

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Should I expect side effects?

The side effects from a third COVID-19 vaccine are similar to those experienced after receiving the original vaccines. Scientists in Israel recently began giving a third dose of the Pfizer-BioNTech vaccine to people with compromised immune systems. Side effects were reported by 31% of people, the most common being soreness at the injection site. Other side effects included fatigue, headache, body aches, and fever. These symptoms don’t last long — about one to three days.

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Should I get a third dose if I’ve had a breakthrough infection after previously being vaccinated?

The safety of a third dose in people who’ve had COVID-19 breakthrough infections is not known, therefore an additional dose for those patients is not recommended at this time. Some patients in whom initial vaccine responses are expected to be severely blunted, such as stem cell transplant or CAR-T recipients or those treated with B-cell depleting therapies, may benefit from a third dose after breakthrough infection. Discuss your situation with your clinical care team.

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After receiving a third dose, what more should I do to protect myself?

Even after the third dose, people with weakened immune system must take precautions to protect themselves from COVID-19. You should:

  • Wear a mask.
  • Stay 6 feet apart from others you don’t live with.
  • Avoid crowds and poorly ventilated indoor spaces until advised otherwise by your healthcare provider.
  • Encourage your close contacts to be vaccinated.

If you develop symptoms of COVID-19, contact your clinical care team and get tested.


September 15, 2021


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