Measles cases in the United States are rising, and parents who reject vaccination are shouldering much of the blame.

Nearly half of the 131 cases so far this year involved unvaccinated children. Fourteen cases were reported in California through the first seven months of this year.

Health officials worry that as vaccination rates decline, herd immunity is lost, increasing the chance of a mass outbreak. Some pediatricians, meanwhile, are frustrated that they have to spend so much time convincing parents that vaccines such as those for measles, mumps and rubella are safe.

Questioning in itself is not a bad thing, especially since the Internet has ignited an explosion of information – much of it inaccurate.

It does, however, reflect a larger crisis of confidence in public health officials and policy, which has developed partly because so many new, seemingly unnecessary vaccines have been added to the schedule and because no one can explain what causes, how to prevent or how to treat the new childhood disorders: asthma, allergies, attention deficit disorder and autism.

The number of vaccines that children receive has tripled since the early 1980s. In 1982, the U.S. Centers for Disease Control and Prevention recommended 23 doses of seven vaccines for children up to age 6.

Today's typical 6-year-old has had 48 doses of 12 vaccines. (Toss in the flu shot, which may or may not be effective, and it boosts the number to 69 doses of 16 vaccines by age 18.)

Immunization against diseases that were once a childhood rite of passage and that conferred lifelong immunity, such as chickenpox, is now required for public school in many states. And the hepatitis B vaccine is routinely given to babies the day after they're born, even though the illness is contracted through blood transfusions and sexual activity. Parents wonder: "Why can't the hep B vaccine wait?"

But what really prompted questions was the 1997 decision by the Food and Drug Administration to remove the mercury-based preservative thimerosal from most vaccines as a precaution, due to concerns about the "theoretical potential for neurotoxicity" and the growing number of vaccines containing thimerosal.

Though no evidence of harm has been shown, a mental link to thimerosal was made, a scarlet letter on vaccines that remains to this day.

Several recent developments have sparked other questions about vaccines.

Dr. Bernadine Healy, the former head of the National Institutes of Health, told CBS News that she thinks "public health officials have been too quick to dismiss the (autism­vaccine) hypothesis as irrational."

In March, government health officials conceded that childhood vaccines aggravated a rare, underlying cellular disorder in a 9-year-old girl from Athens, Ga., that ultimately led to autismlike symptoms.

America might be overvaccinating its kids, and health officials might want to re-evaluate and adjust the immunization schedule, according to a study in the New England Journal of Medicine.

But not because of health concerns; the vaccines might just be unnecessary and a waste of money.

A study in the journal Pediatrics found that 33 percent of pediatricians would strongly recommend the rotavirus vaccine if it were up to the doctor's discretion. But if it becomes an "official" recommendation by the American Academy of Pediatrics, that number goes up to 50 percent.

Last year, a week after CDC announced that the influenza vaccine was effective against only 40 percent of the season's flu viruses, it recommended that all children over 6 months get a flu shot.

Vaccination, considered to be one of medicine's greatest achievements, is a personal decision that is often forced on people for the greater good. Many parents who question vaccines are simply seeking information and advocating for their children.