Vaccines are used to improve your immune system and prevent serious, life-threatening diseases.
HOW VACCINES WORK
Vaccines "teach" your body how to defend itself when germs, such as viruses or bacteria, invade it:
They expose you to a very small, very safe amount of viruses or bacteria that have been weakened or killed.
Your immune system then learns to recognize and attack the infection if you are exposed to it later in life.
As a result, you will not become ill or you may have a milder infection. This is a natural way to deal with infectious diseases.
Four types of vaccines are currently available:
Live virus vaccines use the weakened (or attenuated) form of the virus. The measles, mumps, and rubella (MMR) vaccine and the varicella (chickenpox) vaccine are examples.
Killed (inactivated) vaccines are made from a protein or other small pieces taken from a virus or bacteria. The flu vaccine is an example.
Toxoid vaccines contain a toxin or chemical made by the bacteria or virus. They make you immune to the harmful effects of the infection, instead of to the infection itself. Examples are the diphtheria and tetanus vaccines.
Biosynthetic vaccines contain manmade substances that are very similar to pieces of the virus or bacteria. The Hib (Haemophilus influenzae type B) conjugate vaccine is an example.
WHY WE NEED VACCINES
For a few weeks after they are born, babies have some protection from germs that cause diseases. This protection is passed from their mother through the placenta before birth. After a short period, this natural protection goes away.
Vaccines help protect against many diseases that used to be much more common. Examples include tetanus, diphtheria, mumps, measles, pertussis (whooping cough), meningitis, and polio. Many of these infections can cause serious or life-threatening illnesses and may lead to lifelong disabilities. Because of vaccines, many of these illnesses are now rare.
SAFETY OF VACCINES
Some people worry that vaccines are not safe and may be harmful, especially for children. They may ask their health care provider to wait or even choose not to have the vaccine. But the benefits of vaccines far outweigh their risks.
Scientific studies have shown that vaccines and their components, such as the preservative thimerosal, do not cause autism or ADHD. Based on these studies, the American Academy of Pediatrics, the Centers for Disease Control and Prevention, as well as the Institute of Medicine conclude that the benefits of vaccines outweigh their risks.
Other information about risks:
Getting the actual infection from vaccines: Unless a person's immune system is weakened, it is unlikely that a vaccine will give the person the infection. Vaccines, such as the measles, mumps, rubella, the chickenpox, and nasal spray flu contain live but weakened viruses and should not be received by persons with weakened immune systems.
Allergic reactions: Such reactions are rare and are usually to some part (component) of the vaccine.
Danger of live vaccines: Certain live vaccines may be dangerous to the fetus of a pregnant woman. These include the measles, mumps, rubella vaccine, the chickenpox vaccine, and the nasal spray flu vaccine. To avoid harm to the baby, pregnant women should not receive any of these vaccines. The health care provider can tell you the right time to get these vaccines.
The recommended vaccination (immunization) schedule is updated every 12 months by the U.S. Centers for Disease Control and Prevention (CDC). Talk to your health care provider about specific immunizations for you or your child. Current recommendations are available at the CDC website: http://www.cdc.gov/vaccines/schedules.
The CDC website (http://www.cdc.gov/travel/page/vaccinations.htm) has detailed information on immunizations and other precautions for travelers to other countries. Many immunizations should be received at least one month before travel.
Bring your immunization records with you when you travel internationally. Some countries require this documentation.
Centers for Disease Control and Prevention. Advisory Committee on Immunization Practices (ACIP) Recommended Immunization Schedules for Persons Aged 0 Through 18 Years and Adults Aged 19 Years and Older - United States, 2013. MMWR. 2013;62(Suppl1):1-19.
Centers for Disease Control and Prevention. Vaccine safety and adverse events. Available at http://www.cdc.gov/vaccines/vac-gen/safety/default.htm. Accessed April 19, 2013.
DeStefano F, Price CS, Weintraub ES. Increasing exposure to antibody-stimulating proteins and polysaccharides in vaccines is not associated with risk of autism. J Pediatr. 2013; DOI10.1016/j.peds.2013.02.001.
Institute of Medicine. Immunization Safety Review Committee. Imunization Safety Review: Vaccines and Autism. Washington, DC: The National Academies Press; 2004.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.