Vaccines are a key development in medicine because they enable us to prevent known communicable (highly contagious) diseases before people get sick, rather than just fighting the disease as it appears. While there are many different types of vaccines, they all work in the same basic way. Vaccines introduce illness-causing microbes into the body in a controlled manner in order to trigger an immune system response. The body produces antibodies that would be used to fight an actual infection, which then prepares the immune system to recognize and fight the pathogen more quickly if it appears again. This reaction boosts the immune response in the individual so that if it ever has a real encounter, the person is far less likely to get sick.