Topic 10.1 · Supplement
Passive Immunity
The simplest way to keep active and passive immunity apart under exam pressure: active immunity means your body makes the antibodies; passive immunity means someone else’s body already made them, and you just received them.
Passive immunity is short-term defence against a pathogen using antibodies acquired from another individual, rather than produced by your own immune system in response to an antigen. Because your own lymphocytes never actually encounter and respond to the antigen, none of the mechanism described in active immunity happens here at all — the antibodies simply arrive already made.
The two required examples
Cambridge requires two specific natural routes, both from mother to infant: antibodies passing across the placenta before birth, and antibodies received in breast milk afterwards. Breastfeeding matters biologically for exactly this reason — it continues supplying an infant with ready-made antibodies at a stage when its own immune system is still immature and can’t yet produce sufficient protection on its own.
Why it doesn’t last
Because the antibodies were received rather than produced through the infant’s own immune response, no memory cells are formed. Memory cells are precisely what makes active immunity long-lasting, so their absence here is the direct reason passive immunity is usually temporary rather than long-term. It can offer real, immediate protection — that part shouldn’t be understated — but it isn’t building the same kind of lasting defence that infection or vaccination does.
Active versus passive, side by side
| Feature | Active immunity | Passive immunity |
|---|---|---|
| Source of antibodies | Produced by the person’s own body | Received from another individual |
| How it arises | Infection, or vaccination | Transfer of antibodies — placenta, breast milk |
| Memory cells formed? | Yes | No |
| Duration | Long-term | Usually temporary |
| Example | Immunity after vaccination | Antibodies received in breast milk |
Every row in that table follows from a single fact — whether memory cells are produced or not — so if you’re ever unsure which column a statement belongs in, ask that question first and the rest follows.