From birth, you have received numerous vaccines—hepatitis B, BCG, polio, and more. But do you know why vaccination prevents disease?

The human body has evolved an innate self-protection mechanism—immune function. This system constantly monitors internal changes, distinguishes "self" from "non-self," resists pathogens, and clears internal waste to maintain health.

Immunity is divided into innate (non-specific) immunity and adaptive (specific) immunity.

Innate immunity is the body's natural defense system, present from birth. It targets a broad range of pathogens rather than specific ones—including skin, mucous membranes, antimicrobial substances (e.g., lysozyme), and phagocytes (e.g., macrophages and DCs). The skin's thick keratin layer blocks pathogens, secretions have bactericidal effects, respiratory cilia sweep away foreign particles, and phagocytes engulf and dissolve pathogens.

Adaptive immunity is the third line of defense—acquired after birth through natural infection or artificial immunization (vaccines, toxoids, immunoglobulins). It is specific: stimulated by antigens and reacts specifically to them. For example, recovery from tuberculosis confers specific immunity against TB.

The main effectors are lymphocytes—B lymphocytes bind and clear viruses and bacteria, while T lymphocytes scan all cells and eliminate intracellular pathogens.

Together, innate and adaptive immunity form a protective network, acting as the body's constant health guardians. Now you know the answer: vaccination activates the adaptive immune system, generating specific immunity that enables rapid elimination of invading pathogens.