On Immunity: An Inoculation

by Eula Biss

Infants have all the components of this system at birth. There are certain things the infant immune system does not do well—it has trouble penetrating the sticky coating of the Hib bacteria, for example. But the immune system of a full-term infant is not incomplete or undeveloped. It is what immunologists call “naive.” It has not yet had the opportunity to produce antibodies in response to infection. Infants are born with some antibodies from their mothers already circulating in their systems, and breast milk supplies them with more antibodies, but this “passive immunity” fades as an infant grows, no matter how long it is breast-fed. A vaccine tutors the infant immune system, making it capable of remembering pathogens it has not yet seen. With or without vaccination, the first years of a child’s life are a time of rapid education on immunity—all the runny noses and fevers of those years are the symptoms of a system learning the microbial lexicon.