Vaccinations during childhood cancer treatment — what is safe, what must wait, and what comes next

Yes, but only certain types. Inactivated vaccines — those made from killed viruses or bacteria, or from pieces of a pathogen — are generally considered safe to give during chemotherapy, though the immune response may be weaker than usual. Examples include the inactivated flu shot, the typhoid injection, and hepatitis B. Live vaccines, which contain weakened but living viruses or bacteria, must not be given while a child is receiving chemotherapy or while their immune system remains suppressed. This includes the MMR (measles-mumps-rubella), chickenpox (varicella), nasal-spray flu, rotavirus, and BCG vaccines. Your child's oncology team will tell you exactly which vaccines are permitted at each stage of treatment.

Live vaccines contain weakened versions of real viruses or bacteria. In a healthy child, the immune system recognises and fights the weakened pathogen, building protective memory. In a child whose immune system has been reduced by chemotherapy or other cancer treatment, there is a real risk that even the weakened pathogen in the vaccine could cause an actual infection — because the immune defences that would normally contain it are not functioning properly. The risks vary depending on which vaccine and which treatment the child is receiving, but the principle is consistent: live vaccines are withheld until the oncology team confirms the immune system has recovered sufficiently. This is usually assessed by blood counts and the time elapsed since treatment ended.

Most vaccines given to healthy family members do not pose a risk to an immune-suppressed child. However, there are a few exceptions worth discussing with your team. The oral polio vaccine (OPV), still used in some countries, can shed live virus in stool and is generally avoided in households with an immune-suppressed member — India uses the inactivated injectable polio vaccine in most clinical settings, which does not shed. The nasal-spray flu vaccine (LAIV) can occasionally shed virus too, though the risk is low. Siblings and household contacts should still receive all their routine vaccines on schedule — being protected against measles, chickenpox, flu, and other infections is one of the most important ways to protect your child. Discuss any specific concerns with your oncologist.

In many cases, yes. Chemotherapy can reduce or erase the immunity a child built up from vaccines received before cancer diagnosis. This effect is most pronounced after intensive treatment such as high-dose chemotherapy followed by stem cell transplant, where previously acquired immunity is often substantially reduced. After treatment ends, your child's oncology team will typically recommend a blood test to check antibody levels (titres) for key diseases. Based on the results, a catch-up immunisation schedule will be planned — usually beginning once the immune system has had enough time to recover. The timing and which vaccines are repeated will depend on the treatment your child received and their current blood counts.

The MMR vaccine is a live vaccine and cannot be given until the immune system has adequately recovered after chemotherapy. Most guidelines recommend waiting at least three to six months after the final dose of chemotherapy before giving live vaccines, but this varies by treatment intensity and the child's blood counts. After bone marrow or stem cell transplant, the wait is usually longer — often 12 to 24 months — and involves immune-function testing before live vaccines are reintroduced. Your child's oncology team will advise the right timing based on regular blood tests. Do not give MMR or any other live vaccine without specific clearance from the oncologist.

The inactivated flu injection is generally recommended for children receiving cancer treatment — influenza can cause severe illness in immune-suppressed children, and the vaccine, though it may not provide as strong a response as in a healthy child, still offers meaningful protection. The nasal-spray flu vaccine (LAIV), which is a live attenuated vaccine, should not be used during active treatment. Your child's oncology team may advise a specific time during the treatment cycle when the flu injection is best given — for example, when blood counts are at a higher level between chemotherapy doses. All household contacts and carers should also receive the inactivated flu vaccine each year to protect your child indirectly.