Infection & ResponseDefinitions

Key Definitions

Part of Vaccination and Herd Immunity · GCSE GCSE Biology revision

This definitions covers Key Definitions within Vaccination and Herd Immunity for GCSE Biology. How vaccines work, types of vaccines, population immunity, vaccination programs It is section 10 of 15 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.

Topic position

Section 10 of 15

Practice

21 questions

Recall

12 flashcards

Key Definitions

Vaccination: The process of introducing antigens into the body (via injection or oral administration) to stimulate the immune system to produce memory cells, providing protection against future infection without causing disease.

Vaccine: A preparation containing antigens from a pathogen (dead, attenuated, or as components) that triggers an immune response and memory cell formation when administered.

Herd immunity: Protection of unvaccinated individuals within a population because a sufficiently high proportion of the population is immune, preventing the pathogen from spreading and reaching vulnerable people.

Herd immunity threshold: The minimum proportion of a population that must be immune for herd immunity to be achieved. Calculated as 1 - (1/R₀), where R₀ is the basic reproduction number.

Live attenuated vaccine: A vaccine containing weakened (but living) pathogen that can replicate briefly without causing disease. Produces strong, long-lasting immunity (e.g., MMR vaccine).

Inactivated vaccine: A vaccine containing killed pathogens or pathogen components. Safer for immunocompromised individuals but may require booster doses (e.g., flu vaccine, hepatitis A).

Booster dose: An additional vaccine dose given some time after the initial course to maintain or enhance immunity by restimulating memory cells and increasing antibody levels.

Basic reproduction number (R₀): The average number of new cases one infected individual causes in a fully susceptible population. A higher R₀ means more contagious and a higher vaccination threshold needed for herd immunity.

Keep building this topic

Read this section alongside the surrounding pages in Vaccination and Herd Immunity. That gives you the full topic sequence instead of a single isolated revision point.

How It Works: Why a Weakened Pathogen Creates Real Protection Common Misconceptions Edward Jenner and the Birth of Vaccination Key Facts: Vaccination and Herd Immunity

Practice Questions for Vaccination and Herd Immunity

What do vaccines contain?

A. Live, active pathogens that cause disease
B. Dead or inactive pathogens or their antigens
C. Antibiotics to kill bacteria
D. White blood cells from another person

1 markfoundation

Explain how vaccination protects a person from getting a disease. [3 marks]

3 marksstandard

Quick Recall Flashcards

Why don't vaccines cause the disease they protect against?

Vaccines use dead or inactive pathogens, or just antigens from the pathogen's surface. The pathogen cannot multiply or cause infection. The immune system still recognises the antigens and builds immunity.

What is a vaccine and how does it work?

A vaccine contains a dead or weakened form of a pathogen (or its antigens). It triggers the immune system to produce antibodies and memory cells without causing disease. If the real pathogen enters later, memory cells respond rapidly.

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How It Works: Why a Weakened Pathogen Creates Real Protection

Common Misconceptions