How Do Vaccines Create Immunity?

Vaccines work by mimicking an infection without causing disease. They introduce an antigen — a weakened or inactivated pathogen, a piece of it (like a protein), or its genetic instructions (mRNA) — into the body. The immune system recognises the antigen as foreign and mounts a response: B cells produce antibodies that neutralise the antigen, while T cells destroy infected cells. Crucially, some of these cells become long-lived memory cells. If the real pathogen later enters the body, the immune system recognises it immediately and mounts a rapid, strong response, preventing illness or reducing its severity. This process is the basis of immunological memory.