Immunity and Vaccination

Core concept

When a vaccinated person is later exposed to the real disease-causing pathogen, their immune system already 'remembers' it from the vaccine and can respond quickly and effectively, often preventing illness entirely or making it much milder. Vaccination programs have successfully eliminated or greatly reduced diseases like smallpox and polio worldwide. Herd immunity occurs when enough people in a community are vaccinated, making it harder for a disease to spread, indirectly protecting even those who cannot be vaccinated.