What to Know About Covid-19 Boosters for Cancer Patients

What to Know About Covid-19 Boosters for Cancer Patients

Reviewed by Jasper Clinical Board

Last updated 8/17/21

The Centers for Disease Control and Prevention recently issued new guidance on Covid-19 vaccination for people who are immunocompromised. This guidance applies to most people undergoing active cancer treatment. 
Here’s what you need to know to protect yourself and other people from Covid-19 when you’re immunocompromised.
You might need a third vaccine dose
The CDC now recommends that people who have moderately to severely compromised immune systems and have received two doses of either the Pfizer or Moderna vaccine receive a third dose of the same vaccine. The timing of the third dose should be at least four weeks, or 28 days, after the second dose. 
This guidance applies to people with a variety of health conditions, including: 
  • Those being actively treated for tumors or blood cancers
  • People who have received a stem cell transplant within the last two years, or stem cell transplant recipients who are taking medication to suppress the immune system
  • Those being actively treated with high-dose corticosteroids or other immune-suppressing drugs
  • Organ transplant recipients taking medication to suppress the immune system
  • People with primary immunodeficiency that’s moderate to severe (such as DiGeorge syndrome or Wiskott-Aldrich syndrome)
  • People with advanced or untreated HIV infection
Talk to your healthcare providers about whether the new CDC guidance applies to you. They will be able to advise you about whether you need an additional dose of a Covid-19 vaccine. 
For people who are immunocompromised, it’s important to talk to your healthcare team to get specific advice about getting a third Covid-19 vaccine shot. Some people may need to pause taking immune-suppressing medications to allow the third dose of the vaccine to work. For other people this can be too risky. Your healthcare team can help determine what makes sense for you. 
It’s also worth noting that the Pfizer vaccine is authorized for people aged 12 and older, and the Moderna vaccine is approved for use in those 18 and older, so you need to meet these age requirements in order to get a third dose. 
Immunocompromised people still need to take extra precautions
Even if you get three doses of an mRNA vaccine, if your immune system is significantly compromised, you are still likely to be more vulnerable to Covid-19 infection and to serious illness than others. The CDC advises immunocompromised people to continue taking extra measures to protect themselves even after receiving a third vaccine dose. 
These precautions should include: 
  • Wearing a mask
  • Staying six feet away from people outside your household
  • Avoiding crowds and poorly ventilated spaces
Ensuring anyone you have close contact with who is eligible to get vaccinated does so is another important way to protect yourself from Covid-19.
What’s behind the new CDC advice
The new recommendation for a third mRNA vaccine dose from the CDC is based on a few key data points: 
  • People with moderately to severely compromised immune systems have higher risk for severe illness if they get Covid-19. 
  • Being immunocompromised may also make a person more likely to transmit Covid-19 to others, even if they’ve had two doses of an mRNA vaccine.
  • People who are immunocompromised may need a third vaccine dose for their bodies to build sufficient immunity to Covid-19. This helps protect the immunocompromised person as well as people in their household. 
Vaccines work by training the body’s immune system to respond to invading pathogens. If your  immune system is weakened, it may not create as strong a reaction to a vaccine as a typical immune system. So, in order to gain significant protection from vaccination, you may need an extra dose. 
The CDC cites small studies showing that people with compromised immune systems make up a large share of people hospitalized with Covid-19 “breakthrough” infections. Though people with moderately to severely compromised immune systems make up only 3% of the U.S. population, they represent 40-44% of fully vaccinated people hospitalized with Covid-19.
Cancer treatment and the immune system
A common side effect of cancer treatment is a weakened immune system. Chemotherapy, radiation therapy, stem cell and bone marrow transplants and surgery can all weaken your immune system. So can corticosteroid medications, which can be used to treat cancer or reduce side effects of other cancer treatments. 
Being immunocompromised means you’re more susceptible to infections of all kinds, so it’s important to take steps to protect yourself. In addition to a third Covid-19 vaccination shot, this can include measures like avoiding skin breaks and people with signs of illness, and certain activities and foods. Your healthcare team can give you specific advice based on your situation. 
What else should I know about the CDC’s new guidance? 
The CDC’s recommendation for a third vaccine dose only applies to people who are moderately to severely immunocompromised and received two doses of an mRNA vaccine (either the Pfizer or Moderna shot). 
There is some evidence suggesting that people with compromised immune systems who aren’t fully protected after two doses of an mRNA vaccine may get better protection from Covid-19 after a third mRNA vaccine dose. 
The CDC recommends getting the same mRNA vaccine that you received for your first two doses if it’s available. If it’s not available or you can’t remember which mRNA vaccines you received for your first two shots, you can get either mRNA vaccine for your third dose. 
The CDC says no one should get more than three mRNA vaccine shots. 
For people with compromised immune systems who received the one-dose Johnson & Johnson vaccine, the CDC isn’t currently recommending any additional doses. This is because there isn’t enough data available to suggest that people who got the non-mRNA Johson & Johnson vaccine would benefit from another dose of it, or a dose of an mRNA vaccine.
Talk to your healthcare team if you have questions
If you have any concerns or questions about vaccination or your risk for Covid-19, talk to your healthcare team. They can help you navigate what’s best for you.
Ready to schedule a vaccine? 
You can schedule a Covid-19 vaccine at a Walgreens or CVS near you. Just follow one of the links to get started. Some Walgreens and CVS locations also offer vaccines on a walk-in basis without an appointment. 

The content on this website is intended to provide the best possible information for you, but should not be considered—or used as a substitute for—medical advice. If you have questions about your diagnosis or treatment, please contact your health care provider(s). For questions or comments about this content, please email us at