COVID-19 Vaccine Safety and Side Effects: Important Information for People with Cancer

Man getting a COVID-19 vaccine

We are vaccinating our patients in phases.

Now that more people with cancer are eligible to receive the COVID-19 vaccines, you may have questions about how well they work and what you should expect when you are vaccinated.

Memorial Sloan Kettering is moving as quickly as possible to vaccinate our patients. 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 eligibility here.

Your safety is our top priority. We are constantly reviewing the latest data on COVID-19 vaccines to make the best recommendations for our patients.

Our Chief Medical Epidemiologist Mini Kamboj answers key questions about what we know so far.

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

The initial studies testing the vaccines included very few people who were receiving treatment for cancer. That’s because those studies first needed to see if the vaccines were safe and effective in people with healthy immune systems. Those initial studies showed that the vaccine provides strong protection against COVID-19.

Mini Kamboj

Mini Kamboj

We believe the vaccines are safe. The question is whether they work as well in people having cancer treatment, such as chemotherapy and radiation. Some cancer treatments can reduce how well a person’s immune system responds. It’s possible that the vaccines may not be as effective in those patients. Even so, some protection is better than none.

As we develop detailed guidelines for vaccinating our patients, MSK experts are reviewing the studies and opinions of other major cancer research organizations, too. Every patient’s situation is unique, so you should always talk with your doctor about what’s best for you.

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What about patients with severely weakened immune systems?

There is not a lot of information about how the vaccine works in patients with severely weakened immune systems, such as people who have received a stem cell transplant. We believe the vaccine will be safe for these patients, but it may not work as well during certain phases of cancer treatment. You should discuss the timing of getting a vaccine, as well as the risks and benefits, with your MSK care team.

There are ongoing studies to learn more about how people with weakened immune systems respond to the vaccine. Rest assured that we are staying on top of the very latest information for our patients.

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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.

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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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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.

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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 2, 2021


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