The diseases prevented by the 12 childhood vaccines in the table below are bad ones. They can leave you blind, deaf, or paralyzed. They can cause painful infections of the bones, lungs, or skin. They can inflame the brain, turn healthy cells cancerous, or scar the heart. In some cases, they can kill.

Routine vaccination, however, has all but eliminated many of those diseases. For example, in 2006 there were only 55 reported cases of measles in the U.S., and none of diphtheria or polio. In comparison, before vaccination became common some 500,000 people in the U.S. developed measles each year, 176,000 contracted diphtheria, and 16,000 came down with polio.

Experts hope that current recommendations for the flu and meningitis vaccines, as well as new vaccines against viruses that contribute to certain other common childhood diseases and even cervical cancer, will prove equally successful. And they caution that failure to vaccinate could lead to a resurgence of some previously controlled diseases. Indeed, recent outbreaks of the mumps and pertussis (whooping cough) may have stemmed in part from declining immunity because of inadequate vaccination. In many cases, vaccination rates for more recently recommended vaccines remain low.

But there's little reason for the average person to avoid being vaccinated, because the potential benefit of vaccination greatly outweighs the potential risks. Those risks include the vaccine-specific side effects described in the table below, as well as minor reactions such as mild fever or pain at the injection site, severe but rare allergic reactions, and fainting. (Because of that last risk, the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices now recommends that kids stay in the doctor's office for 15 minutes after getting vaccinated.) See the CDC's vaccination schedule for children ages birth to 6 years old.