Vaccines in Children with a Serious Illness

What are vaccines?

A vaccine helps the immune system learn to defend against germs and illness. A vaccine may keep your child from getting sick. Or your child could have a milder infection than they would have had without the vaccine.

Some vaccines may need 1 or more doses for lifelong protection. Other vaccines, such as the flu shot, may be needed more often.

Childhood vaccine schedules

Routine vaccines are those recommended for everyone. The Centers for Disease Control and Prevention (CDC) lists recommended vaccinations by age for people in the United States. This is known as a vaccine or immunization schedule.

If your child has a weak immune system due to cancer or other serious illness, your care team may recommend changes to your child’s vaccine schedule. For example, cancer patients may need to delay certain vaccines during treatment because of the effects of cancer or chemotherapy. Talk to your care team about vaccine recommendations for your child as well as for family caregivers and household members.

How vaccines work

Vaccines teach the body how to defend itself when specific germs invade it. A vaccine causes an immune response to a certain germ. If the body meets that germ in the future, then the immune system can recognize and fight it better.

Vaccines are very safe and effective for most people. The most common side effects are low-grade fever, fatigue, pain or swelling at the injection site, and headache or body aches. These are usually mild and go away within a few days. Side effects are often a sign that the immune system is building a defense against the disease.

Vaccines in children with weak immune systems

Some children with cancer or other medical conditions are immunocompromised (have weak immune systems). Treatments such as chemotherapy, immunotherapy, radiation therapy, stem cell transplant, and some medicines can weaken the immune system. A vaccine must cause a good immune response to be most effective. Vaccines may not work well in someone with a weak immune system. This is because the weak immune system may not be able to respond fully to the vaccine.

A vaccine can provide some protection against severe illness even in people who are immunocompromised. Children with weak immune systems can generally get all of the routine vaccines except the attenuated, live-virus vaccines.

Live virus vaccines

Some kinds of vaccines contain weakened, live virus. These vaccines may cause illness in patients with very weak immune systems. Patients should not get these vaccines while their immune systems are weak.

Other kinds of vaccines may contain just parts of germs that are already dead. These are different types of vaccines. They do not cause illness because the germs are already dead.

Some routine vaccines are made with live virus. Live virus vaccines that should not usually be given to children with weak immune systems include:

• MMR (measles, mumps, rubella)
• Varicella (chickenpox)
• Rotavirus
• Nasal flu mist

Children with weak immune systems should also avoid anyone who has had:

• A rash after recently getting the chickenpox (varicella) vaccine
• The nasal flu vaccine within 1 week
• An oral (by mouth) polio vaccine (This vaccine is not used in the United States.)

Flu vaccine

The standard flu shot is made with dead flu viruses. It is safe for people with weak immune systems. The CDC recommends a yearly flu vaccine for everyone ages 6 months and older. The flu virus can change over time, so the flu vaccine is slightly different each year. The body’s immune response to the flu goes down over time, so people need another flu shot. 

COVID-19 vaccine

The COVID-19 vaccine is made with dead parts of a virus. It is not a live vaccine, so it is a safe and effective way to prevent COVID-19. If your child is not up to date for vaccination against COVID-19, ask your care team about the vaccine. COVID-19 vaccines are approved or authorized for children ages 6 months and up.

Always talk with your health care provider if you have questions about what kinds of vaccines your child can take.

When to resume normal vaccines

Your child’s care team will let you know when to vaccinate your child and what vaccines are needed. This will depend on your child’s treatments and their medical needs.

After chemotherapy: In general, your child may resume vaccinations at least 3 months after the end of chemotherapy. They can follow a catch-up vaccination schedule. A catch-up schedule is for children whose vaccinations have been delayed. Even if your child had some routine vaccinations during chemotherapy, they should generally have a catch-up schedule as if the vaccines had not been given. This is because it is not known whether the vaccines were fully effective.

After B-cell antibody therapy: Patients treated with anti B-cell antibodies should wait at least 6 months before starting vaccinations again.

After stem cell (bone marrow) transplant: Transplant patients may have to wait longer. Transplants wipe out the immune defenses that a person had before treatment. If your child has had a transplant, they will need to get new vaccinations. Your care team will tell you when your child is ready to start vaccinations after transplant.

Vaccines for family and household members

If your child has a weak immune system, they can have more trouble fighting germs. They may have a higher risk of severe complications from illnesses such as the flu and COVID-19. They may not be able to get certain vaccines or vaccines may not work as well.

It is important for household members and those in close contact with your child to get the flu vaccine. Family and caregiver vaccinations help to create a circle of protection around your child. This lowers the chances that your child will be exposed to a disease that a vaccine can stop.

Questions to ask your care team

• Which vaccines does my child need?
• When is the best time for my child to be vaccinated?
• How does my child’s medical condition or treatment affect their immune response?
• How does my child’s medical condition or treatment affect their vaccine schedule?
• Are there any vaccines my child should not get?
• What should we expect before, during, and after getting vaccines?
• What vaccines do family members need?

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