Vaccines work by presenting a harmless piece of a pathogen to the immune system. This trains the body to recognize and respond quickly if it encounters the real pathogen later.
The immune response
When the immune system sees a foreign antigen, it produces antibodies and activates T cells. Some of these become memory cells, which remain in the body for years or even decades. If the pathogen returns, the memory response is faster and stronger.
Types of vaccines
Traditional vaccines use weakened or inactivated viruses. mRNA vaccines give cells instructions to make a viral protein temporarily. Viral-vector vaccines use a harmless virus to deliver genetic material. All aim to present the same antigen to the immune system.
Safety and effectiveness
Vaccines undergo rigorous clinical trials before approval. Side effects are usually mild and temporary. The benefit of preventing severe disease far outweighs the small risk for most people.