Explain and describe how vaccinations prevent illness.

Vaccinations involve introducing a small amount of dead or inactive form of a pathogen into the body. This stimulates white blood cells to produce complementary antibodies to destroy the pathogen. This is called a primary immune response. When the same pathogen re-enters the body, a secondary immune response is triggered, and specific white blood cells rapidly divide by mitosis and produce vast amounts of the complementary antibody to destroy the pathogen before symptoms occur. Vaccinations can also prevent illness via herd immunity. This occurs when a significant proportion of the population is vaccinated against a disease, the occurrence of the disease is reduce, therefore protecting those who are not vaccinated as well.