This is a medical question of type : prevention 
 how vaccines prevent disease 
 Why Are Childhood Vaccines So Important? It is always better to prevent a disease than to treat it after it occurs. Diseases that used to be common in this country and around the world, including polio, measles, diphtheria, pertussis (whooping cough), rubella (German measles), mumps, tetanus, rotavirus and Haemophilus influenzae type b (Hib) can now be prevented by vaccination. Thanks to a vaccine, one of the most terrible diseases in history – smallpox – no longer exists outside the laboratory. Over the years vaccines have prevented countless cases of disease and saved millions of lives. Immunity Protects us From Disease Immunity is the body’s way of preventing disease.  Children are born with an immune system composed of cells, glands, organs, and fluids located throughout the body. The immune system recognizes germs that enter the body as "foreign invaders” (called antigens) and produces proteins called antibodies to fight them. The first time a child is infected with a specific antigen (say measles virus), the immune system produces antibodies designed to fight it. This takes time . . . usually the immune system can’t work fast enough to prevent the antigen from causing disease, so the child still gets sick.  However, the immune system “remembers” that antigen. If it ever enters the body again, even after many years, the immune system can produce antibodies fast enough to keep it from causing disease a second time. This protection is called immunity. It would be nice if there were a way to give children immunity to a disease without their having to get sick first. In fact there is: Vaccines contain the same antigens (or parts of antigens) that cause diseases. For example, measles vaccine contains measles virus. But the antigens in vaccines are either killed, or weakened to the point that they don’t cause disease. However, they are strong enough to make the immune system produce antibodies that lead to immunity. In other words, a vaccine is a safer substitute for a child’s first exposure to a disease. The child gets protection without having to get sick. Through vaccination, children can develop immunity without suffering from the actual diseases that vaccines prevent. Top of Page More Facts Newborn babies are immune to many diseases because they have antibodies they got from their mothers. However, this immunity goes away during the first year of life. If an unvaccinated child is exposed to a disease germ, the child's body may not be strong enough to fight the disease. Before vaccines, many children died from diseases that vaccines now prevent, such as whooping cough, measles, and polio. Those same germs exist today, but because babies are protected by vaccines, we don’t see these diseases nearly as often. Immunizing individual children also helps to protect the health of our community, especially those people who cannot be immunized (children who are too young to be vaccinated, or those who can’t receive certain vaccines for medical reasons), and the small proportion of people who don’t respond to a particular vaccine. Vaccine-preventable diseases have a costly impact, resulting in doctor's visits, hospitalizations, and premature deaths. Sick children can also cause parents to lose time from work.   Related Pages Why Immunize? Vaccines: A Safe Choice Parents Guide to Immunizations For Parents: How Vaccines Prevent Diseases Top of Page   Images and logos on this website which are trademarked/copyrighted or used with permission of the trademark/copyright or logo holder are not in the public domain. These images and logos have been licensed for or used with permission in the materials provided on this website. The materials in the form presented on this website may be used without seeking further permission. Any other use of trademarked/copyrighted images or logos requires permission from the trademark/copyright holder...more This graphic notice means that you are leaving an HHS Web site. For more information, please see the Exit Notification and Disclaimer policy.