Are Vaccines Safe and Effective if I am on Chemotherapy?

Published: February 03, 2023
Alex Shantiai
By Alex Shayan Shantiai, 2023 PharmD Candidate

For vaccines to be safe and effective for use, it is important that our body’s immune system is functioning properly. Medications to treat cancer, called chemotherapy, work by attacking cancer cells but sometimes, they also can destroy the cells in our body that help our immune system detect and fight infections. This damage to the immune system may mean that vaccines won’t work as well. And for some vaccines, it may not be safe for you to get them either.

How do vaccines work?

Your immune system is primed to detect and attack a pathogen, such as a virus or bacteria, by recognizing a certain marker on the pathogen, called an antigen. Older vaccines work by containing a weakened part of the antigen or an inactivated antigen. Some newer vaccines work by providing a map for producing an antigen similar to the one produced by the pathogen.

No matter the vaccine type, efficacy of the vaccine is dependent on your body’s immune system detecting this antigen and using the immune system to produce a response to it that then gets stored in your cell memory so that if you come in contact with the pathogen in the future, your body can recognize it quickly and prevent you from getting the disease.

In situations where your body’s immune system does not work as well, including by taking chemotherapy, your body may not produce the immune response, or it may need extra doses to produce as much of a response.

For live attenuated vaccines, the small amount of antigen is not enough to cause illness for most of the population. However, for people with weakened immune systems, such as those receiving certain chemotherapy, you may actually get sick from the vaccine and so these types of vaccines are usually not recommended at all.

If I receive chemotherapy, when should I receive a vaccine?

This largely depends on the type of chemotherapy you are receiving and the type of vaccine. Your doctor may recommend you receive important vaccines before you start chemotherapy. For some vaccines, your doctor may recommend you wait for a certain period after you finish chemotherapy before you receive them.

It is important to talk to your doctor before you receive any vaccines while you are on chemotherapy.

Should I stop chemotherapy during flu season?

Your doctor or pharmacist can discuss the recommendations that will help you stay safe. You should never stop your chemotherapy without the advice of your doctor.

You may still receive the COVID-19 vaccine during therapy as even some immune response may help prevent severe hospitalization or worse. Once your chemotherapy is complete, it will be recommended to receive a booster to your COVID-19 vaccine.

The Centers for Disease Control and Prevention recommends that it is safe to receive the flu vaccine 14 days prior to starting chemotherapy, possibly between chemotherapy cycles depending on your circumstances, and three months after completing chemotherapy.


If you are on chemotherapy medications, talk to your doctor or pharmacist before getting any vaccines. Don’t stop chemotherapy before talking to your doctor first.

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