If you think your child gets a lot more shots than you did as a child, you're right. While you might have been vaccinated against about half a dozen diseases, today most children are vaccinated against 14 different diseases by the time they turn two.  By the time your child turns 18, he or she might be vaccinated against two more diseases, receive several booster shots, and get yearly flu shots as well. 

Often a series of two to five doses of a single or combination vaccine (containing vaccines for several different diseases) is needed to create full immunity to a disease. These doses might be given over several months or years. Vaccines help infants and children to develop immunity to dangerous diseases before they might be exposed to them through contact with caretakers, playmates, or family members. Tween and teen vaccines help prevent infections spread through close contact with their peers, such as bacterial meningitis. 

Although they have dramatically reduced the spread of infectious diseases worldwide, vaccines have also attracted controversy over the years. Most vaccine concerns center on either specific vaccine ingredients, or the number of vaccines that children now receive. In 1998, a British doctor published a paper suggesting that the measles-mumps-rubella (MMR) vaccine might cause autism. As a result, people began questioning the safety of different vaccine ingredients, such as the modified virus or bacteria used to create each vaccine, and the mercury-based preservative used in vaccines (this preservative has been removed from most childhood vaccines since 2001). Many scientific papers published since 1998, including a 2004 study by the Institute of Medicine, have not found a link between vaccines and autism. (And that researcher has been thoroughly discredited.)

Many parents still question vaccines, however. Some parents delay vaccines because they believe that the amount of vaccines that young children receive can harm their immune system. Other parents skip vaccines that they think are unnecessary, such as the chickenpox (varicella) vaccine. In most cases, though, it's best to follow the recommended vaccination schedule. A young child's immune system, tested daily by what he or she breathes, touches, or swallows, is robust enough to handle the small amount of modified germs and other ingredients in vaccines. Skipping or delaying vaccines can leave a child unprotected from serious diseases for stretches of time.  Furthermore, if an unvaccinated child catches a vaccine-preventable disease, he might pass on the infection to others. Talk to your child's doctor if you have questions or concerns about vaccinations. You can also find more information about vaccines online on trusted health sites (such as the Mayo Clinic or WebMD), immunization organization sites (such as Every Child by Two or the Children's Hospital of Philadelphia's Vaccine Education Center), or government health agency sites (such as the CDC). On the CDC's website, you can look up the current child and teen vaccination schedule (updated every January), or take a quiz to find out what vaccines your older child (or you) might need.

Laurie Bouck is a health writer, mother, and co-author of The Complete Idiot’s Guide to Vaccinations. She writes about health on her blog, MedFly.