Passive immunitySpec 10.1.13, 10.1.14, 10.1.15
In short
Passive immunity is a short-term defence against a pathogen by antibodies acquired from another individual. A baby receives antibodies from its mother across the placenta before birth and in breast milk after birth. No memory cells are produced and the antibodies are broken down, so the protection does not last.
Passive immunity is a short-term defence against a pathogen by antibodies acquired from another individual. The person's own lymphocytes do not make the antibodies.
Antibodies pass from mother to baby across the placenta before birth, and in breast milk after birth.
Breast-feeding is important for passive immunity in infants. The baby's immune system is not yet fully developed, and antibodies in the milk protect the baby against pathogens, for example in the gut.
Memory cells are not produced in passive immunity. The antibodies are broken down, so the protection is short-term and the baby is not protected if the pathogen returns later.
| Active immunity | Passive immunity | |
|---|---|---|
| Antibodies made by | The person's own lymphocytes | Another individual (passed on) |
| Source | Infection or vaccination | Placenta or breast milk |
| Memory cells | Produced | Not produced |
| Length of protection | Long-term | Short-term |
The key contrast is memory cells. No memory cells means short-term protection.
Quick check
What is an antibody?
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A protein that binds to a specific antigen.
What gives long-term immunity after vaccination?
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Memory cells.
Name two ways a baby gets antibodies from its mother.
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Across the placenta and in breast milk.
Why is passive immunity short-term?
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No memory cells are produced.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026