How do vaccines work?
Vaccines work by training the immune system to recognize a germ without causing the disease. If the real germ attacks later, the body can fight it quickly.
A vaccine contains a weakened or killed germ, a piece of it such as a protein, or instructions for cells to make that piece, as in mRNA vaccines. The immune system reacts by making antibodies and special white blood cells. It also creates memory cells that remember the germ for months, years or a lifetime.
When a vaccinated person is exposed to the real germ, their immune system recognizes it and responds rapidly, often preventing illness or making it much milder. Some vaccines need booster doses to keep protection strong. Common side effects, like a sore arm or mild fever, show the immune system is responding.
Protecting communities
When enough people in a community are vaccinated, germs have trouble spreading, which protects people who cannot be vaccinated, such as newborns. This is called community or herd immunity. Vaccines helped eradicate smallpox in 1980 and have greatly reduced diseases like polio and measles.
Did You Know?
The first vaccine was developed by English doctor Edward Jenner in 1796, using cowpox to protect against smallpox. The word vaccine comes from the Latin vacca, meaning cow.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.