Natural, artificial, active and passive immunity

Microbiology, Immunity and Forensics · The immune response · note 4 of 5

Spec 6.11

A Level only

A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels mean

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Natural, artificial, active and passive immunitySpec 6.11

In short

In active immunity the body makes its own antibodies and memory cells, after infection (natural) or vaccination (artificial). In passive immunity ready-made antibodies are received, across the placenta or in breast milk (natural) or by injection (artificial). Passive immunity is immediate but short-lived.

Types of immunity
Type	How it develops	Example
Natural active	Infection by a pathogen: the body makes antibodies and memory cells	Recovering from chickenpox
Natural passive	Antibodies pass from mother to baby: IgG across the placenta, and IgA in colostrum and breast milk	Newborn protected by mother's antibodies
Artificial active	Vaccination: weakened or inactivated pathogen, or its antigens, are given and the body makes antibodies and memory cells	MMR vaccine, tetanus vaccine
Artificial passive	Injection of ready-made antibodies from another person or animal	Antivenom after a snake bite; tetanus immunoglobulin after a deep wound

Active compared with passive immunity
Feature	Active	Passive
Antibodies made by	The person's own plasma cells	Another person or animal
Memory cells formed	Yes	No
Time to protection	Days to weeks (primary response)	Immediate
Length of protection	Long-lasting (years or life)	Short (weeks to months) as antibodies are broken down

Vaccines contain antigens but do not cause the disease. They stimulate the primary response, so memory cells are in place. If the real pathogen is met later, the secondary response is fast enough to prevent symptoms. Vaccination of a high proportion of the population also protects those who are not vaccinated, because the pathogen has fewer people to spread between (herd immunity).

Common mistake:

'Natural' and 'artificial' describe how the antibodies or antigens get in (infection or mother, versus medicine). 'Active' and 'passive' describe whether the person makes their own antibodies. Do not mix these up.

Written and checked against the Edexcel International A Level Biology (YBI11) specification · Updated October 2026

Frequently asked questions

What is the difference between innate and adaptive immunity?

Innate (non-specific) responses such as inflammation, lysozyme, interferon and phagocytosis act against any pathogen, quickly and in the same way. The adaptive (specific) response uses B and T cells whose receptors are complementary to one antigen, takes days at first, and produces memory cells for faster future responses.

How do antibodies work?

Antibodies are Y-shaped proteins made by plasma cells. The variable region on each arm has a shape complementary to one antigen. They bind to pathogens and toxins, clump pathogens together (agglutination), make them easier for phagocytes to engulf, and block attachment to host cells.

What do T helper cells and T killer cells do?

T helper cells are activated by antigen-presenting cells and release cytokines that stimulate B cells and T killer cells. T killer cells destroy body cells that display the antigen, such as virus-infected cells, by releasing perforin and enzymes. Both types also form T memory cells.

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