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3.10 Vaccination

How a vaccine of dead or inactive pathogen makes lymphocytes produce antibodies and memory cells, why this gives immunity, how herd immunity protects people who are not vaccinated, and the advantages and disadvantages of vaccination.

AQA Edexcel OCR 2 min read

What a vaccine is

Key terms

  • Vaccine: a small amount of a dead or inactive form of a pathogen (or just its antigens), given to make the body immune.
  • Immunity: the ability to destroy a pathogen quickly, before it causes illness, because memory cells are present.
  • Herd immunity: when so many people in a population are immune that a pathogen cannot spread, protecting those who are not immune.

How vaccination works

How vaccination works: an inactive pathogen is injected, lymphocytes make antibodies and memory cells, and a later infection is destroyed quickly
How vaccination works: an inactive pathogen is injected, lymphocytes make antibodies and memory cells, and a later infection is destroyed quickly
  1. A small quantity of a dead or inactive form of the pathogen is put into the body, usually by injection. It cannot cause the disease, but it still carries the pathogen's antigens.
  2. The antigens stimulate lymphocytes to make antibodies against them.
  3. Memory lymphocytes are also made, and stay in the blood.
  4. If the real pathogen enters the body later, the memory cells recognise its antigens and the lymphocytes make the right antibodies quickly and in large amounts. The pathogen is destroyed before the person becomes ill.

Some vaccines need a booster dose later to keep the number of memory cells high.

Herd immunity

If a large proportion of a population is vaccinated, the pathogen has very few people it can infect, so it cannot spread. This protects people who cannot be vaccinated, such as young babies and people with weak immune systems.

Herd immunity: when few people are vaccinated a disease spreads widely; when most are vaccinated it cannot spread, protecting unvaccinated people too
Herd immunity: when few people are vaccinated a disease spreads widely; when most are vaccinated it cannot spread, protecting unvaccinated people too

Advantages and disadvantages

Vaccination: for and against
AdvantagesDisadvantages
Has controlled many serious diseases, such as polio and measles, and wiped out smallpoxVaccines do not always give immunity
Prevents epidemics through herd immunitySome people have side effects, such as swelling or a fever; serious reactions are very rare
Cheaper to prevent a disease than to treat itSome pathogens change their antigens quickly (such as flu), so a new vaccine is needed every year

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