How do vaccines work?

A vaccine works by safely introducing your immune system to a part of a pathogen — such as a weakened or inactivated virus, a protein from its surface, or genetic instructions to make that protein (as in mRNA vaccines). Your body responds by producing antibodies and memory cells, without you having to suffer the actual disease. If you later encounter the real germ, your immune system recognizes it and mounts a fast, strong defense, often preventing illness entirely. When enough people are vaccinated, diseases struggle to spread — a protective effect called herd immunity that also shields those who cannot be vaccinated. Vaccines have saved hundreds of millions of lives.