Immunizations are vaccines made of either weakened or “killed” versions of the bacteria or virus that causes a particular disease. When these altered viruses and bacteria are injected or taken orally, the immune system mounts an attack that stimulates the body to produce antibodies.Once produced, the antibodies remain active in the body, ready to fight off the real disease. For example, if whooping cough broke out in your area, an immunized child would be much less likely to contract the disease than one who wasn’t immunized.

Immunizations are designed to protect against serious illnesses ranging from polio and tetanus to measles, mumps, and the seasonal flu. Many people consider them the most important part of well-child checkups.

Every year, the U.S. Centers for Disease Control’s Advisory Committee on Immunization Practices publishes a new schedule showing which vaccines are recommended and when to get them. This schedule is endorsed by the American Academy of Pediatrics and the American Academy of Family Physicians.

What’s new this year?

* The committee now recommends “combination vaccines,” meaning that an immunization containing more than one vaccine is preferable to giving each vaccine separately.
* A yearly dose of H1N1 flu vaccine has been added to the schedule for children 6 months and older.
* The fourth dose of the polio vaccine should be given after age 4 and at least six months after the previous dose.
* A newer HPV vaccine that prevents genital warts is now an option for girls; it’s also an option for boys age 9 to 18, but isn’t on the recommended schedule.

If your child has gotten behind on immunizations, ask your doctor about the “catch-up” schedule.

DTaP, to protect against diphtheria, tetanus, and pertussis (whooping cough):
• At 2 months
• At 4 months
• At 6 months
• Between 15 and 18 months (can be given as early as 12 months as long as it’s at least six months after the previous shot)
• Between 4 and 6 years old
• A booster shot at 11 or 12 years of age

Hepatitis A, to protect against hepatitis A, which can cause the liver disease hepatitis.
• Between 12 and 23 months, two shots at least six months apart

Hepatitis B (HBV), to protect against hepatitis B, which can cause the liver disease hepatitis:
• At birth
• Between 1 and 2 months
• Between 6 and 18 months.

Hib, to protect against Haemophilus influenza type B, which can lead to meningitis, pneumonia, and epiglottitis:
• At 2 months
• At 4 months
• At 6 months (not needed if the PedvaxHIB or ComVax brand of vaccine was given at 2 and 4 months)
• Between 12 and 15 months

HPV, to protect against human papillomavirus, the most common sexually transmitted disease in the United States and a cause of cervical cancer:
• Three doses between 11 and 12 years, for girls (one version of the HPV vaccine prevents genital warts in males, but isn’t on the official schedule)

Influenza (the flu shot or, for age 2 and up, nasal spray vaccine); two doses to protect against H1N1 flu and one to protect against seasonal flu:
• Age 6 months and up, every year in the fall or early winter

Meningococcal, to protect against meningococcal disease, the leading cause of bacterial meningitis in U.S. children in pre-vaccine days:
• Between 11 and 12 years

MMR, to protect against measles, mumps, and rubella (German measles):
• Between 12 and 15 months
• Between 4 and 6 years old

Pneumococcal (PCV), to protect against pneumococcal disease, which can lead to meningitis, pneumonia, and ear infections:
• At 2 months
• At 4 months
• At 6 months
• Between 12 and 15 months

Polio (IPV), to protect against polio:
• At 2 months
• At 4 months
• Between 6 and 18 months
• Between 4 and 6 years old

Rotavirus, to protect against rotavirus, which can cause severe diarrhea, vomiting, fever, and dehydration (given orally, not as an injection):
• At 2 months
• At 4 months
• At 6 months (not needed if the Rotarix brand of vaccine was given at 2 and 4 months)

Varicella, to protect against chicken pox:
• Between 12 and 15 months
• Between 4 and 6 years.