Explain why passive immunity provides only short-term protection against disease, whilst active immunity provides long-term protection.

Passive immunity gives only short‑term protection because it relies on antibodies that are transferred from another individual or source; these antibodies are eventually degraded and are not produced by the recipient’s immune system, so no memory cells are formed.

In contrast, active immunity involves the recipient’s own immune system recognising the antigen and producing specific antibodies. This process generates memory B and T cells that persist for years. When the same antigen re‑enters the body, these memory cells recognise it immediately and trigger a rapid, robust antibody response, providing long‑term protection.