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In easy-to-understand language
Note: The terms "immunization," "vaccination," and "inoculation" are used to mean essentially the same thing throughout this site.
Benefits of Vaccines

Disease prevention is the key to public health. It is always better to prevent a disease than to treat it. Vaccines prevent disease in the people who receive them and protect those who come into contact with an unvaccinated individual. In the United States, Federal and State public health programs help assure that children receive vaccines. But vaccines are not just for young children. Adolescents and adults should keep up-to-date on certain immunizations. Unvaccinated adults who did not have certain childhood diseases should consider being immunized. And, people who travel overseas may receive vaccines depending on their destinations.

Once scientists have identified the microorganism or toxin that causes an illness, they pursue a number of approaches to develop a vaccine. All approaches to vaccine development focus on the immune system and the body�s natural defenses against foreign invaders. The immune system is a complex of organs and highly specialized cells and even a circulatory system separate from blood vessels all of which work together to clear infection from the body. The purpose of a vaccine is to bring about immunity by provoking a response from a person�s immune system and creating a memory within the immune system so that exposure to the active disease agent will stimulate an already primed immune system to fight the disease.

Basic Research and Development

Basic research conducted and supported by the National Institutes of Health�s (NIH) National Institute of Allergy and Infectious Diseases (NIAID), and basic and applied research at the Food and Drug Administration�s (FDA) Center for Biologics Evaluation and Research (CBER) are helping scientists understand more about infectious microbes and human immune responses. From this understanding has come development of vaccines and other tools needed to prevent many infectious diseases and immune system disorders. The goal of these efforts is not only to protect individuals from serious infections, but eventually to eradicate diseases, as we have done with smallpox.

Basic research focuses on the biological mechanisms disease-causing microbes use to cause damage. Such research also takes into account physical characteristics of an organism, which might be used as a vaccine component, or as a drug to prevent or interrupt the disease process.

To develop a candidate vaccine, scientists first test preparations in cell-culture or tissue-culture systems. If initial results are promising, the candidates are further tested in laboratory animals such as mice, guinea pigs or even monkeys. In some cases, computers can help researchers visualize the vaccine candidates in three dimensions to predict how vaccines will interact with the immune system. If the vaccine candidate performs well throughout these preclinical evaluations, it can become an investigational vaccine for use in human volunteers in clinical trials.

Clinical Studies

Clinical studies rely upon the participation of thousands of people, from all walks of life, who volunteer their time and energy to advance science and improve health care for all. A typical volunteer in a vaccine study agrees to be given the vaccine, makes frequent visits to a clinic for evaluation, participates in medical testing, and provides blood or tissue samples that will be used in assessing the vaccine�s safety and potential effectiveness. Research staff counsel volunteers about the study, and volunteers must sign an informed consent document, indicating their understanding of the study and their willingness to participate.

NIAID has designed a network of vaccine and treatment evaluation units, and more recently, an international network for testing vaccines to prevent infection with HIV. Testing sites are based at leading university medical research centers, public health departments, and community clinics. Investigators working within these networks and other NIAID-supported researchers play major roles in the clinical studies required for licensing of vaccines.

A candidate vaccine undergoes three phases of clinical trials before it can be considered for approval. Then FDA can approve a vaccine for general use if it is safe, effective in preventing an infectious disease, and remains stable and potent during its shelf life. The overall risk/benefit of a vaccine is critical in making a licensure decision.

Side Effects and Adverse Reactions

No matter how extensive the testing, it is impossible to allow completely for the infinite variation among individuals, their immune systems, and their reactions to the introduction of new substances into their bodies. Serious systemic reactions to vaccines can occur, although they are very rare. The FDA and the Centers for Disease Control and Prevention (CDC) monitor vaccine distribution and use and collect information on adverse reactions to vaccines, even after they are licensed for use by the general public.

Vaccines of the Future

Vaccines remain among the most powerful tools we have for disease prevention, and advances in biotechnology have ushered in a new era in vaccine development that holds even more promise for improving public health. Currently scientists are pursuing many promising new strategies in vaccine development and exploring novel ways to administer vaccines that may provide safer, more effective ways to fight disease.

NIH, National Institute of Allergy and Infectious Diseases:

Last updated: August 2001

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