Why Cancer Patients Should Be Vaccinated against COVID-19 and What Is Safe Afterwards

Man getting a COVID-19 vaccine

We are vaccinating our patients in phases.

Memorial Sloan Kettering recommends cancer patients be vaccinated against COVID-19, and we are moving as quickly as possible to distribute the vaccines. Supply is limited, and we must follow federal, New York State, and New York City guidelines. We are proceeding in phases. You can learn more about your eligibility here.

The Centers for Disease Control and Prevention (CDC) reports as of March 8, 2021, more than 92 million vaccine doses have been administered in the US and no concerns for serious adverse reactions or side effects have emerged.

There is a lot of good information available from credible sources like the CDC demonstrating the safety and effectiveness of the COVID-19 vaccines, but there is also misinformation circulating, particularly on social media.  

It’s important to know that none of the COVID-19 vaccines interact with or alter your DNA in any way. They cannot cause cancer.

Our Chief Medical Epidemiologist Mini Kamboj offers the facts and answers questions you may have about the COVID-19 vaccine and cancer.

Is the vaccine safe for people in active treatment for their cancer?

Mini Kamboj

Mini Kamboj

The evidence demonstrates the COVID-19 vaccines are safe, and we are recommending our patients with cancer be vaccinated. Some cancer treatments like chemotherapy or radiation can reduce how well a person’s immune system responds. Therefore, it’s possible that the COVID-19 vaccines may not be as effective in those patients. Even so, our experts strongly believe some protection against COVID-19 is better than none.

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What about cancer patients with severely weakened immune systems?

We believe the COVID-19 vaccines will be safe for patients with severely weakened immune systems, for example, as the result of a stem cell transplant. But these vaccines may not work as well during certain phases of cancer treatment. You should discuss the timing of getting a COVID-19 vaccine as well as the risks and benefits with your MSK care team.

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Do I still need to follow safety guidelines even after I’ve been vaccinated?

Yes. It’s important to continue to wear a mask, wash your hands often, and practice social distancing.

This is especially true right after you get the vaccine because it takes time for your immune system to respond and offer protection. These practices are very important even after you have developed immunity. The vaccine protects you from getting sick, but we still don’t know if people can carry and spread the virus after getting vaccinated.

Although the CDC recently issued updated guidance saying that fully vaccinated people can gather at home in small groups without masks or social distancing, this guidance does not apply to healthcare settings like MSK or to people with cancer who are at higher risk of disease.  

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How effective are the COVID-19 vaccines?

There are currently three COVID-19 vaccines that have been given emergency authorization by the US Food and Drug Administration. The Pfizer-BioNTech, Moderna, and Johnson & Johnson/Janssen vaccines have all been found to be highly effective and safe after large studies involving a broad range of ages and ethnic groups.

All three COVID-19 vaccines provide strong protection against severe disease, hospitalization, and death from COVID-19.

The Pfizer-BioNTech vaccine was 95% effective in its study involving about 43,000 people. The Moderna vaccine was 94% effective in a study involving more than 30,000 people. The Johnson & Johnson/Janssen vaccine was 85% effective in preventing severe COVID-19 in a study of more than 44,000 people.

These impressive results hold true as tens of millions of Americans have been vaccinated.

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I’ve read that one of the possible side effects of the vaccine could be mistaken for cancer. What do I need to know?

Some patients who receive the vaccine may experience swelling or tenderness in their lymph nodes. It is also possible that this swelling will show up on imaging tests and could be mistaken for the progression of certain cancers — primarily breast, head and neck, melanoma, and lymphoma.

The swelling is usually noticed within two to four days after the vaccination and can last for an average of ten days. On imaging tests, the lymph node enlargement may be detected for a longer period. For these reasons, we recommend:

  • If you develop this symptom after you’re vaccinated, you should speak to your doctor. Most of the time, they will recommend that you wait at least four weeks before getting further tests to give time for the swelling to disappear.
  • You should schedule your COVID-19 vaccination after any routine imaging. If you’ve already had the vaccine, we recommend you wait six weeks for any routine breast screenings, including mammography and breast MRI.
  • If you’ve had cancer, you should ask for your COVID-19 vaccine to be administered on the opposite side of your cancer diagnosis if possible.
  • If you have any discomfort from the swelling, you can use a warm compress. Acetaminophen or nonsteroidal anti-inflammatory drugs may be taken to ease the discomfort.

It’s important to know that all kinds of vaccines can cause temporary swelling of the lymph nodes, which may be a sign that the body is making antibodies in response as intended.

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What are other possible side effects?

Some people have mild to moderate side effects, but they don’t last long — about one to three days. The most common side effects include soreness at the injection site, fatigue (feeling tired), headache, body aches, and fever. These side effects are more common after the second dose, and you may need extra rest. Severe side effects are rare and treatable with medications like Tylenol or Advil. It’s important that you do not take these drugs before getting your vaccine, as there are some potential concerns that some pain relievers may interfere with the immune response to the vaccine. It’s also unclear if taking medication ahead of time actually works to reduce vaccine symptoms.

Getting vaccinated will not make you sick with the virus that causes COVID-19.

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How can I be assured the COVID-19 vaccines are safe?

According to the CDC, more than 92 million vaccine doses have been given to Americans as of March 8, 2021, and no concerns for serious adverse reactions or side effects have emerged.

There is incorrect information from unreliable sources on social media about how the Pfizer-BioNTech and Moderna vaccines use something called Messenger RNA (mRNA). The facts are that there are thousands of different kinds of mRNA in human cells. Each kind of mRNA does different things. It’s important to know mRNA is not the same as DNA and cannot be combined with DNA to change your genetic code.

Here’s how the mRNA vaccines work: They use a tiny piece of the coronavirus’s genetic code to teach your immune system how to make a protein that will trigger an immune response if you get infected. The mRNA is fragile, so after it delivers the instructions to your cells, it breaks down and disappears from the body in about 72 hours. The mRNA never even goes into the nucleus of the cell — the part that contains your DNA.

The vaccines do not cause cancer. They do not expose you to the virus that causes COVID-19. You cannot get COVID-19 or any other infection from the vaccine.

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Should cancer survivors get vaccinated against COVID-19?

Yes. We believe the vaccine is safe, effective, and offers critical protection to keep cancer survivors in good health. New York State guidelines recommend vaccination for people with active cancer and for those in remission. If you are a New York State resident who was treated for cancer in the past, you can find more information here about how you can get vaccinated. If you live outside New York State, you can find more information here.

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Learn why it’s so important to keep taking steps to protect yourself and others from COVID-19.
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Will the vaccine affect my cancer treatment?

There is no evidence that the vaccine will affect your treatment, but you should discuss any concerns with your doctor.

The most important thing to remember during this pandemic is that cancer patients should continue treatment. We have taken every precaution to make sure you can receive your therapy in a safe environment. Cancer care is essential care, and we don’t want our patients to put their lifesaving treatments on hold.


March 12, 2021


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