Can vaccines overload my baby’s immune system?

Short Answer

No evidence suggests that the recommended childhood vaccines can “overload” the immune system. Studies demonstrate that infants’ immune systems can handle receiving many vaccines at once—more than the number currently recommended. In contrast, from the moment babies are born, they are exposed to numerous bacteria and viruses on a daily basis. Eating food introduces new bacteria into the body. Infants put their hands and other objects into their mouths many times every hour, exposing them to still more antigens (foreign substances that induce an immune response). All of these routine activities amount to more work for a baby’s immune system than the recommended vaccine schedule.


From the time babies leave the womb they are colonized with trillions of bacteria, requiring them to constantly make antibodies to protect themselves from infection. Children are also exposed to a variety of viruses that can cause runny noses, congestion, cough, fever, and diarrhea. The immunological components in vaccines today are miniscule compared with the immunological challenges that infants handle every day.

The immunization schedule currently used is based on infants’ ability to generate immune responses, as well as when they are at risk of certain illnesses. For example, the immunity passed from mother to child at birth is only temporary, and typically does not include immunity against polio, hepatitis B, Haemophilus Influenzae type B, and other diseases that can be prevented by vaccination.

Although children receive more vaccines now than ever before, the number of immunological components in vaccines has dramatically decreased. Thirty years ago, children received seven vaccines that contained more than 3,000 bacterial and viral proteins. Today, there are only about 150 in 14 vaccines.