Ground zero in the debate is the pediatrician's office.
Among those taking a stand are the eight pediatricians of Northwestern Children's Practice in Chicago. They no longer see children whose parents refuse to follow the childhood immunization schedule developed by the Centers for Disease Control and Prevention and the American Academy of Pediatrics. A letter and email sent to parents this year announced the policy, which went into effect in June.
"All of the available research shows that the safest and most effective way to vaccinate children is on the schedule set by the CDC and AAP," said Dr. Scott Goldstein, one of the pediatricians. "To go against that schedule goes against proven scientific research and puts patients who do follow the schedule at risk."
So far, fewer than a dozen families have chosen to leave the practice of about 5,000 to 6,000 patients, said Goldstein, who participates in the Illinois Immunization Patient Advocacy Leadership Initiative run by the Illinois chapter of the AAP.
Statistics show that the vast majority of parents support vaccination, regarded by many physicians as one of the greatest success stories in public health. But the number of parents resisting shots for their children has been increasing.
"Our data clearly shows that in most counties, the percentage of parents seeking (vaccine) waivers has gone up over the last 10 years," said Dr. Douglas S. Diekema, referring to statistics from his home state of Washington. "I think that reflects what's going on in the nation."
Diekema, lead author of an AAP policy paper, Responding to Parental Refusals of Immunization of Children, said it's too early to know if the trend will continue because statistics were gathered before the medical journal Lancet more than a year ago retracted a highly publicized study that suggested that the measles, mumps and rubella vaccine could cause autism.
The 1998 report by Dr. Andrew Wakefield, whose British medical license was revoked last year, had an immediate impact on vaccination rates. A study last year in the journal Pediatrics reported that about 12 percent of parents have declined at least one recommended vaccine.
Of those who refused a vaccine, human papilloma was the most commonly refused, followed by varicella (chickenpox), meningococcal conjugate and MMR.
Diekema said vaccine refusals deeply trouble many physicians. About 5 percent to 10 percent of pediatricians have discharged a family if, after educational efforts, parents still withheld permission for an immunization, he said.
But the AAP and its Illinois chapter encourage pediatricians to continue to provide care to children whose parents are unwilling to follow the vaccination schedule.
"Families with doubts about immunization should still have access to good medical care, and maintaining the relationship in the face of disagreement conveys respect and at the same time allows the child access to medical care," the AAP policy states. "Furthermore, a continuing relationship allows additional opportunity to discuss the issue of immunization over time."
Unvaccinated children are vulnerable to potentially fatal but preventable diseases, and they also can put the health of others at risk.
This year, the U.S. has recorded the highest number of measles cases since 1996: 118 through May, according to the CDC. Most of the cases were linked to people who got measles overseas, and most, but not all, were unvaccinated.
Overall, vaccination rates remain high in Illinois schools, at 98 percent. But a recent Tribune analysis of public and private schools found that the immunization rate against certain diseases fell below 60 percent in some schools, and the number of schools below 90 percent for measles, mumps, polio, rubella or the diphtheria, tetanus, pertussis vaccination more than doubled between 2003 and 2010, from 83 to 198.
Health officials aim for an immunization rate of no lower than 90 percent in order to prevent epidemics, and say clusters of unvaccinated people weaken the "herd immunity" made possible through vaccines. That raises the risk of disease outbreaks.
Those who cannot be vaccinated, such as infants too young to get all their shots and children with underlying medical problems, rely on herd immunity, as do children who have gotten their shots but don't develop immunity.
Dr. Minal Giri, medical director of Melrose Park Pediatrics, said only a handful of parents expressed concern after her medical practice implemented a vaccine policy in fall 2008.
"The impetus behind the policy was to protect our patients," she said. "We have newborns, we have pregnant moms, we have kids with cancer who are immune-compromised, and it is a risk for them to have people coming in who have not been vaccinated."
Experts say educating parents is paramount.
"Pediatricians need to do a better job of letting parents know the risks of not getting vaccinated," Diekema said. "Parents don't have a lot of first-hand experience with these diseases anymore."