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Vaccinations and Serious Childhood Illness

Can children with serious childhood illnesses get vaccines?

Depending on your child’s treatment or diagnosis, your care team may have recommendations about vaccines. For example, childhood cancer patients may need to delay certain vaccines during cancer treatment because of the effects of cancer or chemotherapy.

Routine vaccines are those recommended for everyone in U.S. The Centers for Disease Control (CDC) publishes a recommended childhood vaccination schedule each year. You might also hear vaccines called immunizations.

How vaccines work

Vaccines teach the body how to defend itself when specific germs invade it.

Vaccines make the body’s defense system develop a response to that germ so that the body can recognize and fight it if exposed in the future. The immune system then learns to remember the germ and can recognize and attack it if the person is exposed to it later.

This means you may not become ill or could have a milder infection.

Giving vaccines to people who are around a at risk person can also help prevent that person from being exposed to the germ.

Vaccines and weakened immune systems

Some seriously ill children have weakened immune systems.

A vaccine requires a good immune response to be effective. Vaccines may not be as effective when given to someone who has a weakened immune system. The weakened immune system cannot respond normally by creating a memory of the germ. That means it may not be able to attack it later.

Vaccines that contain weakened virus can cause patients with very weakened immune systems to become sick if they receive them. Patients should not get these vaccines while their immune systems are weak.

The routine vaccines that should not usually be given to people with a weakened immune system include:

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

Vaccine recommendations

The Infectious Diseases Society of America recommends an annual flu shot for all children older than 6 months. People need a flu shot once a year because the makeup of the flu shot is different each year. Influenza viruses are constantly changing. The body’s immune response decreases over time.

Children with weakened immune systems should not receive the flu mist nasal vaccine because it contains live virus.

The flu shot is made with dead flu viruses. It is safe for people with weakened immune systems. It may be given at least 2 weeks before chemotherapy or between chemotherapy cycles.

Transplant, cellular (CAR T-cell) therapy, and gene therapy patients may get a flu shot 6 months after their infusion. If there is an influenza outbreak in the community, they may receive a flu shot 4 months after transplant.

Exceptions to these rules would be patients who are not likely to respond to the flu vaccine, although they are unlikely to be harmed by it. Patients not likely to respond include those who have received strong chemotherapy or those who have received anti B-cell antibodies within 6 months.

Children who have weakened immune systems can generally receive all of the routine vaccines except the attenuated virus vaccines.

If your child has not completed their routine vaccines, you can talk with your child’s care team.

When to resume normal vaccines

Your child’s care team will let you know when to vaccinate your child. Your child may be immunized with vaccines with inactivated virus and live vaccines for chickenpox and MMR.

In general, patients may resume vaccinations at least 3 months after the end of chemotherapy. They can follow a catch-up schedule. A catch-up schedule is for children whose vaccinations have been delayed.

Patients who received anti B-cell antibodies should wait at least 6 months before resuming vaccinations.

Transplant patients may have to wait longer. They will need to receive all new vaccinations because the transplant process has wiped out the immune system they had before the transplant. Their care team will let them know when they are ready to start vaccinations.

Patients who received some routine vaccinations during chemotherapy should generally have a catch-up schedule as if those had not been given. This is because it is not known whether the vaccinations were effective or not.

Male child holding arm up with big smile after being vaccinated

Children need to receive all immunizations allowed by their primary care provider.

Vaccines for siblings and family members

Siblings and adults who live with a child with a weakened immune system should keep current on vaccinations to minimize the chances of exposing the child to a vaccine-preventable disease.

People in the household should not receive the oral polio vaccine. (This vaccine is not used in the United States.)

If an infant in the household has recently received rotavirus vaccination, all family members should wash hands thoroughly and frequently after contact with the vaccinated infant, especially when changing diapers.

Transplant patients and those receiving cancer therapy should not change diapers at all.

Children with weakened immune systems should avoid any person who has had:

  • A rash after recently receiving the chickenpox (varicella) vaccine
  • The nasal flu vaccine within one week

For more information about vaccinations, visit:

Key points

  • Your child’s care team might have vaccine recommendations if your child has a weakened immune system.
  • Routine vaccines are safe and effective.
  • Follow your care team’s vaccine instructions exactly. 

Reviewed: October 2022