Why do we get shots when visiting the doctor? How do vaccines work with our immune systems to keep us from getting sick?

From NOVA PBS: Immunity and Vaccines Explained.

Our bodies are bombarded by bacteria and viruses. For those that make their way inside, our immune system is on guard, waiting not only to kill the invaders but also to create memory cells that will help defeat them more quickly the next time they try to attack. Vaccines, which are weakened versions of a disease like polio or measles, rely on the memory of our immune system to combat the real danger if it eventually enters our bodies.

Related watching: Cell vs. virus: A battle for health, Flu Attack! How A Virus Invades Your Body, and ew! The beautiful physics and math of sneezes.

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