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The immune system and vaccination
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Your body has several lines of defence against pathogens. Vaccines train it in advance.
Physical and chemical barriers
Skin: a physical barrier. Mucus and cilia trap and remove pathogens in the airways.
Stomach acid kills pathogens in food. Lysozyme in tears breaks down bacterial cell walls.
Stomach acid kills pathogens in food. Lysozyme in tears breaks down bacterial cell walls.
White blood cells
Lymphocytes make antibodies that fit antigens on a specific pathogen.
After infection, memory lymphocytes remain. A second infection triggers a faster, bigger response, so you do not become ill: immunity.
After infection, memory lymphocytes remain. A second infection triggers a faster, bigger response, so you do not become ill: immunity.
Vaccination
A vaccine contains a dead or harmless form of the pathogen.
Lymphocytes respond and make memory cells without you becoming ill.
If enough people are vaccinated, the pathogen struggles to spread: herd immunity.
Lymphocytes respond and make memory cells without you becoming ill.
If enough people are vaccinated, the pathogen struggles to spread: herd immunity.
Why does a second infection by the same pathogen usually not make you ill?
- Memory lymphocytes remember the antigen.
- They produce antibodies faster and in larger amounts.
- The pathogen is destroyed before symptoms develop.
Answer: Memory cells give a fast, strong response.
Barriers keep pathogens out. Lymphocytes make antibodies specific to antigens and leave memory cells. Vaccines create memory cells safely; herd immunity protects others.
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