How do vaccines stimulate immunity?

Vaccines stimulate immunity primarily by using weakened or deactivated forms of pathogens. When a vaccine is administered, it introduces a form of the pathogen that is unable to cause disease, whether due to being killed or modified so that it cannot replicate. This exposure trains the immune system to recognize and respond to the specific features of the pathogen, particularly the antigens on its surface.

Upon exposure to the vaccine, the immune system generates a response that includes the production of antibodies and the activation of T-cells, creating a memory of the pathogen. This memory enables the immune system to respond more swiftly and effectively if it encounters the actual pathogen in the future. This process forms the basis of adaptive immunity, where the body can respond faster and more efficiently to subsequent infections with the real pathogen.

The introduction of live, active pathogens would pose a risk of causing disease, and providing antibiotics does not engage the immune response in the way vaccines do. Creating a physical barrier against pathogens is not the mechanism through which vaccines operate, as their role is to prime the immune system rather than prevent initial exposure directly.