Vaccines and Immunizations

Basics and Common Questions:

How Vaccines Prevent Disease
Previously titled "How Do Vaccines Work?

Parents are naturally concerned about the health and safety of their children. The popularity of preventive measures from child-proof door latches to auto safety seats are evidence of their concern. Illness and death caused by infectious diseases, while not as widespread as a half-century ago, are still a danger. Vaccines protect children by preparing their bodies to fight many potentially deadly diseases.

Disease Prevention--Protect Those Around You

Disease prevention is key to public health. It is always better to prevent a disease than to treat it. Vaccines can protect both the people who receive them and those with whom they come in contact. Vaccines are responsible for the control of many infectious diseases that were once common in this country and around the world, including polio, measles, diphtheria, pertussis (whooping cough), rubella (German measles), mumps, tetanus, and Haemophilus influenzae type b (Hib). Vaccine eradicated smallpox, one of the most devastating diseases in history. Over the years vaccines have prevented countless cases of infectious diseases and saved literally millions of lives.

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.

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, or antigens, and produces protein substances called antibodies to fight them. A normal, healthy immune system can produce millions of these antibodies to defend against thousands of attacks every day, doing it so naturally that people are not even aware it is happening. Antibodies often disappear once they have destroyed the invading antigens, but the cells involved in antibody production remain and become "memory cells." Memory cells remember the original antigen and then defend against it if the same antigen attempts to re-infect a person, even after many decades. This protection is called immunity.

Vaccines contain the same antigens or parts of antigens that cause diseases, but the antigens in vaccines are either killed or greatly weakened. Vaccine antigens are not strong enough to cause disease but they are strong enough to make the immune system produce antibodies against them. Memory cells prevent re-infection when they encounter that disease again in the future. Through vaccination, children develop immunity without suffering from the actual diseases that vaccines prevent.

Why are Childhood Vaccines So Important?

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. Also, young children do not have this "maternal immunity" against some diseases, such as whooping cough.
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 now protected by vaccines, we do not 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. These include children who are too young to be vaccinated (for example, children less than a year old cannot receive the measles vaccine but can be infected by the measles virus), those who cannot be vaccinated for medical reasons (for example, children with leukemia), and those who cannot make an adequate response to vaccination.

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This page last modified on April 25, 2012
Content last reviewed on April 25, 2012
Content Source: National Center for Immunization and Respiratory Diseases

Page Located on the Web at http://www.cdc.gov/vaccines/vac-gen/howvpd.htm