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Diseases reference index «Immunizations - general overview»

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

See also: Babies and shots



When germs such as viruses or bacteria invade your body, your immune system makes special cells. These cells produce antibodies, which help destroy these germs. If all goes well, you get better. The next time your body is exposed to the same infection, your immune system often recognizes it and sets out to destroy it.

Immunizations work in much the same way. 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.

Newborns, babies, and toddlers are constantly being exposed to germs from: their parents and 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 from their mother because some antibodies are passed from the mother to the baby through the placenta before birth. After this short period of time, these infections can cause severe illnesses in children and adults.

After immunizations were introduced on a wide scale, infections such as tetanus, diphtheria, mumps, measles, pertussis (whooping cough), and polio became rare. Newer immunizations have also decreased certain types of meningitis, pneumonia, and ear infections in children.

Four different types of vaccines are currently available.

  • Attenuated (weakened) live virus is used in the measles, mumps, and rubella (MMR) vaccine and the varicella (chickenpox) vaccine.
  • Killed (inactivated) vaccines are made from a protein or other small pieces taken from a virus or bacteria. These vaccines are safe, even in people with weakened immune systems. 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, rather than to the infection itself. Examples are the diphtheria and tetanus vaccines.
  • Biosynthetic vaccines contain human-made substances that the immune system thinks are infectious organisms. The Hib (Haemophilus influenzae type B) conjugate vaccine is one example.


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 the small amount of mercury (called thimerosal) that is a common preservative in multidose vaccines causes autism or ADHD. However, studies have NOT shown this risk to be true.

The American Academy of Pediatrics, and The Institute of Medicine (IOM) agree that no vaccine or component 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.

All of the routine childhood vaccines are available in single-dose forms that do not contain added mercury.

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

Other risks 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.

Like many medications, there is always the chance that an immunization can cause side effects. However, deciding not to immunize a child also involves risk. The potential benefits from receiving vaccines far outweigh the potential risks.

After immunizations were introduced on a wide scale, infections such as tetanus, diphtheria, mumps, measles, pertussis (whooping cough), and polio became rare. All of these illnesses used to lead to lifetime disabilities, or even death.

Newer immunizations have also decreased certain types of meningitis, pneumonia, and ear infections in children.

Pregnant women may contract an infection that can be very dangerous to their fetus.


The recommended immunization schedule is updated at least every 12 months by organizations such as the American Academy of Pediatrics. Consult 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 (www.cdc.gov) 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:

  • Chickenpox - vaccine
  • DTaP immunization (vaccine)
  • H1N1 (swine) influenza vaccine
  • Hepatitis A vaccine
  • Hepatitis B vaccine
  • Hib - vaccine
  • Influenza vaccine
  • MMR - vaccine
  • Pneumococcal conjugate vaccine
  • Pneumococcal polysaccharide vaccine
  • Polio immunization (vaccine)
  • Tdap vaccine
  • Tetanus - vaccine

Alternative Names

Vaccinations; Immunizations - safety; How immunizations work

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