After receiving a vaccine for a viral infection, Maria is exposed to the actual virus. What principle of adaptive immunity allows her body to respond more effectively to this exposure compared to someone who hasn't been vaccinated?

After vaccination, Maria’s immune system has already learned to recognize the virus’s specific proteins, creating memory B and T cells that remember the pathogen. When she later encounters the real virus, these memory cells are quickly reactivated and multiply, producing a rapid, strong, and specific immune response. This memory response is much faster and stronger than the primary response that a person without vaccination would need to build from scratch. For example, if Maria’s memory B cells recognize the viral spike protein, they will instantly produce large amounts of antibodies that neutralize the virus before it can spread, whereas a non‑vaccinated person would take days to produce the same antibodies. The key principle is adaptive immunity’s memory, which turns a future encounter into a swift, targeted defense.