Immunizations - general overview

Immunization (vaccination) is a way to trigger your immune system and prevent serious, life-threatening diseases.

See also: Babies and shots



Immunizations 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 a virus or bacteria that has 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 either not become ill or have a milder infection. This is a natural way to deal with infectious diseases.

Four different 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 of this type.
  • Killed (inactivated) vaccines are made from a protein or other small pieces taken from a virus or bacteria. Influenza shots are an example of this type of vaccine.
  • 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 human-made substances are very similar to pieces of the virus or bacteria. The Hib (Haemophilus influenzae type B) conjugate vaccine is one example.


Newborns, babies, and toddlers are constantly being exposed to germs from their parents, other adults, brothers and sisters, people in stores, and other children in child care. With travel easier than ever, you and your baby can be exposed to diseases from other countries without you knowing.

For a few weeks after they are born, babies will have some protection, which was passed from their mother through the placenta before birth. After a short period of time, this natural protection goes away.

Immunizations help protect infants, children, and adults against many infections that used to be much more common.

  • Examples include tetanus, diphtheria, mumps, measles, pertussis (whooping cough), meningitis, and polio.
  • Newer immunizations protect children and adults against other types of meningitis, pneumonia, and ear infections.

Many of these infections can cause serious or life-threatening illnesses, and may lead to lifelong disabilities. Because of immunizations, all of these illnesses are now rare.


Many parents are worried that some vaccines are not safe and may harm their baby or young child. They may ask their doctor or nurse to wait, or even refuse to have the vaccine. However, it is important to also think about the risks of not having the vaccination.

Some people believe that vaccines cause autism or ADHD. They are worried that a small amount of mercury (called thimerosal) that is used as a preservative in multidose vaccines will cause these problems. Multidose means that many doses of vaccine come in one bottle.

However, studies have NOT shown this risk to be true.

  • Experts such as The American Academy of Pediatrics, and The Institute of Medicine (IOM) agree that no vaccine or part of any vaccine is responsible for the number of children who are currently being diagnosed with autism.
  • They conclude that the benefits of vaccines outweigh the risks.

If you are still worried about the risk of autism or ADHD, ask your doctor or nurse about single-dose forms of the vaccine. All of the routine childhood vaccines are available in single-dose forms, and they do not contain added mercury.

The Centers for Disease Control and Prevention website provides further information.

Other risks you may have heard about include:

  • Some parents are worried that they or their child can get the infection from some vaccines, such as the MMR, chickenpox (varicella), or nasal spray flu vaccines. However, unless you have a weakened immune system, this is very unlikely.
  • Although very rare, allergic reactions to some part of the vaccines are possible.
  • Certain live vaccines may be very dangerous to the fetus of a pregnant woman. These include: the measles, mumps, and rubella (MMR) vaccine, the varicella (chickenpox) vaccine, and the Flu-Mist nasal spray vaccine.

Like many medications, there is always the chance that an immunization can cause side effects. However, deciding not to immunize yourself or a child puts both of you at risk for serious infections. The potential benefits from receiving vaccines far outweigh the potential risks.


The recommended immunization schedule is updated at least every 12 months by organizations such as the American Academy of Pediatrics. Talk to your primary care provider about specific immunizations for you or your child. The current recommendations are available on the Centers for Disease Control and Prevention (CDC) website. At every doctor visit, ask about the next recommended immunizations.

Immunizations are not only for children. Each year the CDC posts recommended adult immunizations on their website. Go there to learn about tetanus booster shots, the flu shot, hepatitis A and B vaccines, the pneumococcal vaccine, MMR, and immunizations for chickenpox and meningitis.


The CDC website ( gives travelers detailed information on immunizations and other precautions. Many immunizations should be obtained at least a month before travel.

Remember to take your immunization records with you when you travel internationally. Some countries require this documentation.

See also:

Alternative Names

Vaccinations; Immunizations - safety; How immunizations work


Centers for Disease Control and Prevention. 2012 immunization schedules for children 0 to 18 years of age. October 25, 2011.

Centers for Disease Control and Prevention. Recommended adult immunization schedule United States, 2011. Proposed Revisions, Advisory Committee on Immunization Practices. October 28, 2010.

Updated: 4/15/2012

Reviewed by: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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