Vaccines (immunizations) - overview


Vaccines are used to boost your immune system and prevent serious, life-threatening diseases.

Alternative Names

Vaccinations; Immunizations; Immunize; Vaccine shots



Vaccines "teach" your body how to defend itself when germs, such as viruses or bacteria, invade it:

Four types of vaccines are currently available:


For a few weeks after birth, 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 health problems. Because of vaccines, many of these illnesses are now rare.


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.

The American Academy of Pediatrics, the Centers for Disease Control and Prevention, and the Institute of Medicine all conclude that the benefits of vaccines outweigh their risks.

Vaccines, such as the measles, mumps, rubella, chickenpox, and nasal spray flu vaccines contain live but weakened viruses:

Thimerosal is a preservative that was found in most vaccines in the past. But now:

Allergic reactions are rare and are usually to some part (component) of the vaccine.


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:


The CDC website ( has detailed information about immunizations and other precautions for travelers to other countries. Many immunizations should be received at least 1 month before travel.

Bring your immunization record with you when you travel to other countries. Some countries require this record.



Centers for Disease Control and Prevention. Frequently asked questions about thimerosal (ethylmercury). Updated August 20, 2014. Available at Accessed August 30, 2014.

Centers for Disease Control and Prevention. Immunization schedules. Available at Accessed August 30, 2014.

Centers for Disease Control and Prevention. Vaccine safety and adverse events. Available at Accessed  August 30, 2014.

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. Immunization Safety Review: Vaccines and Autism. Washington, DC: The National Academies Press; 2004.

Orenstein WA, Atkinson WL. Immunization. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 17.