Vaccines work inside and outside the body

“Vaccines work in two ways,” says Tara Haelle, a science and health journalist, and the co-author of The Informed Parent: A Science-Based Resource to Your Child’s First Four Years. “In an individual, the body makes antibodies in response to the vaccine against the disease. That standing army of antibodies then waits. If the pathogen they’re trained to fight arrives, they attack it before an infection takes hold. But the ‘outside’ mechanism is just as important — widespread vaccination reduces the ability of a disease to circulate.”

Known as“herd immunity,” this outside mechanism protects the community, particularly the most vulnerable, those who cannot be immunized because they’re too young or too sick, or have a weak immune system.