Cambridge O Level Biology · Syllabus 5090 · Disease and Immunity
Vaccination
What is Vaccination?
The introduction of pathogen antigens into the body, in a form that does not cause the disease, so that specific lymphocytes respond, antibodies are produced and memory cells are formed. Vaccination therefore stimulates active immunity; it does not supply ready-made antibodies, and it is preventive rather than a treatment for an infection already present.
This definition is part of the Disease and Immunity chapter in Cambridge O Level Biology.
Vaccination in context
A pathogen is a disease-causing organism, and a transmissible disease is one in which the pathogen can pass from one host to another. Every method of disease control in this chapter works by breaking one specific link in the chain that runs from an infected host, along a route of transmission, past the body's barriers, into a new host. Vaccination is the one control that acts on the far end of the chain: it prepares the immune system before the pathogen ever arrives.
Common mistakes with Vaccination
- "Vaccination gives passive immunity." A vaccine supplies antigens, not antibodies, and your own lymphocytes do the work. Write Vaccination stimulates active immunity: the person's own lymphocytes produce antibodies and memory cells are formed.
- "If enough people are vaccinated, nobody can catch the disease." High coverage reduces transmission. It does not make an unvaccinated person immune, and it does not guarantee zero transmission. Write High vaccination coverage reduces the number of susceptible hosts, so chains of transmission are interrupted more often, indirectly protecting some people who cannot be vaccinated.
Questions students ask about Vaccination
Can I say "herd immunity" in an answer?
The safer route is to describe the mechanism rather than rely on a term: high vaccination coverage reduces the number of susceptible hosts, so chains of transmission are interrupted more often, indirectly protecting people who cannot be vaccinated. A described mechanism always scores; a term may or may not be on the mark scheme.