Everything on the GCSE Biology Vaccination & Herd Immunity poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
How vaccines work
A vaccine contains a small amount of a dead or weakened pathogen. When injected, it triggers an immune response without causing disease.
- The vaccine carries the pathogen's antigens into your body.
- Lymphocytes detect the antigens and produce specific antibodies.
- The pathogen is destroyed before it can make you ill.
- Memory lymphocytes stay in the blood, ready for the real pathogen.
Primary vs secondary response
When you are first exposed to an antigen, the primary response is slow. Antibody concentration rises gradually, and by the time enough antibodies are made, you may feel ill.
During re-infection (secondary response), memory lymphocytes recognise the antigen instantly. Antibodies are produced much faster and in much larger amounts, so the pathogen is destroyed before symptoms develop and you are less likely to get ill.
On a graph of antibody concentration over time, the secondary response peak is much higher and faster than the primary response peak.
Herd immunity
If most of a population is vaccinated, the pathogen has very few hosts to infect. It cannot spread easily, so even unvaccinated people (babies, immunocompromised people) are protected.
Outbreaks return when vaccination rates drop.
Examples
- MMR (measles, mumps, rubella)
- Polio
- Meningitis
- HPV
- Flu