Behind the rhetoric, though, a nagging doubt remains among some: Could the science be wrong? Could vaccines cause developmental or other long-term health problems for their children?
Washington state leads the nation in the percentage of parents opting out of vaccinations for their kindergarten-age children. This meant 6.2 percent of these children were missing one or more immunizations in the 2009-10 school year, according to the federal Centers for Disease Control and Prevention.
The immunization most commonly skipped for the state's kindergartners is varicella, which protects against chickenpox.
Since 1997, there's been a steady, statewide decline in the number of school children from kindergarten through high school who are fully vaccinated.
"The world has changed," said Dr. Jack Stephens, a pediatrician at The Everett Clinic. "It used to be the unimmunized child was the child of an economically disadvantaged family with poor access to health care.
"Nowadays, it's usually well-educated parents of higher social status who do their own independent research and tell you what they're willing to do."
And the reasons for skipping or delaying vaccinations vary from family to family. For 32-year-old Maria Rippo of Bothell, the issue is concern about what vaccinations could do to her children. She has chosen to have her four children receive only one vaccine, which protects against diphtheria, tetanus and whooping cough.
"Some people feel we're the enemy because we're not vaccinating," she said.
A new state law that went into effect July 22 seeks to close a loophole that many parents used to avoid providing proof of vaccinations to schools. All they had to do was sign a piece of paper saying they had religious, medical or personal objections to vaccines.
Now, parents must meet with a medical provider, get a signed letter confirming that the consultation took place, and provide the note to child-care centers or schools. That could mean an extra cost to parents of about $90 to $100.
Children who aren't fully immunized can be sent home during outbreaks of a disease for which they have not been vaccinated.
No vaccine is 100 percent effective. But vaccinating most of a population creates a firewall against the spread of contagious diseases.
"This isn't about protecting one child; it's about protecting the entire community," said Dr. Gary Goldbaum, health officer for the Snohomish Health District.
Parents worry about issues such as the number of shots given during any one clinic visit, the number of shots infants receive during their first two years of life and whether immunizations could cause learning disabilities such as autism.
Nationally, more than three-quarters of parents have at least one such question or concern about their child's vaccines, said Glen Nowak, a senior adviser who specializes in immunization and respiratory disease issues for the CDC.
"Our point of view is immunizations … are one of top medical achievements of all time," he said. "They work really well at preventing illness and disease."
Nationally, more than 10 million vaccines are given each year to children less than a year old. The number of recommended vaccinations for children -- now at 16 -- is the largest it's ever been, he said. At some clinic visits, children can get as many as five or six injections.
In pushing for the change in Washington's law, health officials note that vaccine-preventable diseases have been increasing. More than 600 cases of whooping cough were reported in Washington last year, a doubling from the previous year. Most cases were among children 18 and under.
Questions over the safety of vaccines came into the mainstream in the late 1990s, triggered by international debate over a claimed association between the vaccine for measles, mumps and rubella and autism.
Actress Jenny McCarthy became a fiery advocate for the cause, blaming her own son's autism on the vaccine. The movement quickly gained momentum from parents who wanted to protect their children from a severe developmental disorder for which there is still no known cause.
Last year, the British Medical Journal, which originally published a study on the alleged autism-vaccine link in 1998, took the unusual step of retracting the paper, citing the falsification of data in the study and calling its conclusions "fraudulent."
Still, individuals and organizations concerned about vaccine safety point to the National Vaccine Injury Compensation Program as proof that vaccines sometimes have unwanted side effects.
Data from the federal website show that just over $2 billion has been paid out since 1989 in legal cases claiming problems associated with vaccines.
Rippo noted one such recent settlement, which could reach $61 million. "Yes, it does happen, people's lives are ruined," she said.
Yet a report of a problem associated with the vaccine is not proof that the vaccine caused a health problem, such as hospitalizations or death, scientists note. In short, it's hard to prove cause and effect, in part because millions are vaccinated with no long-term health problems.
When vaccine lawsuits reach the courts, juries often sympathize with families, said Stephens, The Everett Clinic pediatrician. "Sitting at one table is a vaccine manufacturer and at the other is a disabled child. Who does your heart go out to?"
Doubt still remains. "My half-sister's grandchild became autistic at 2 years old after a round of vaccines," Rippo said. "But the doctors say there is no way to know if it was caused by the vaccines."
Stephens said there is no link between vaccines and autism. "People still believe it. Once the belief is out there, it takes on a life of is own. It becomes immortal."
To many in the room, Seattle physician Marvin M. Brooke must have seemed like a character who jumped straight out of the grainy black-and-white newsreels of the 1950s.
Here was someone for whom polio was not just a historic reference in a school textbook. "I happened to have polio before the vaccine was tested," he said.
Brooke spoke to a packed room at the Shoreline Conference Center earlier this month, part of a day-long meeting on immunizations organized by the CDC.
Brooke, 62, grew up in Atlanta. He vividly remembers a physician examining him as a 5-year-old in their family home. "I had a stiff neck," Brooke said. "He knew it was polio."
The physician gave a worried, knowing glance at his father. "My father had been a Navy commander," Brooke said. "When you see people like that turn pale, you know it's not good."
Brooke was hospitalized from early September until late December 1954. At the time, up to 10 percent of those with the paralytic form of the disease died from it, he said.
"In my case, there was a risk family members and friends might have gotten polio from me, but they quickly got immunized," Brooke said. "I think people were very glad that scientists were working on vaccines."
Dr. Jonas Salk, who pioneered the polio vaccine, was hailed as a national hero for his breakthrough discovery. For decades, children afflicted with polio battled the disease by being put into long cylindrical tubes called iron lungs. Salk's discovery ended that. Some called him "The Man Who Saved The Children."
Brooke, however, was left with a lifelong partial paralysis of his left arm by polio.
It was a combination of his personal and professional experiences that motivated him to speak out at the immunization meeting.
"I want to make sure we do a good job educating the public," Brooke said. "The result of living with the effects of disease for decades is so big."
Sitting just a few tables away from Brooke at the Shoreline meeting was Maria Rippo. Her children are what she calls minimally vaccinated. "DPT, that's all," she said. The shot, also known as the DTaP vaccine, protects against diphtheria, tetanus and whooping cough, also known as pertussis.
She said she attended the meeting because she hoped to have a true exchange of ideas with other people that day, many of whom were medical professionals.
Rippo said the decision on what vaccines she would allow her children to have "is the hardest decision I made as a parent."
Earlier this year, she traveled to Olympia with the four children, ages 6 to 14, to testify against the state's new immunization law. Rippo said she thinks parents should have a choice on which vaccines to administer to their own children.
"I would love to find an alternative to vaccines that are potentially safer," she said.
She said her family puts a premium on healthy eating and lifestyles to build strong immune systems. "My children rarely miss school due to being sick," she said.
The family grows many of its own vegetables in front and side yard gardens, including salad greens, carrots, squash, strawberries, snap beans and tomatoes. They're starting what they hope will grow into a flock of 10 to 12 chickens for fresh eggs.
Her husband, Tobin Rippo, supplements their meals by hunting for duck, geese, elk, deer and pheasant. He fishes salmon, tuna, halibut, lingcod, snapper and crab.
"We shouldn't be judged about what we decide is the best thing to do for our children," Rippo said. "We shouldn't parent blindly.
"I think more parents worry about vaccine safety than we know," she said. "These are all things to think about, consider and talk to your doctor about."
The story of what was happening at a Pierce County school illustrates why health officials called for change in the state's immunization law.
The goal was to get students enrolled. If the parents didn't have a copy of their child's immunization records, one of the school's employees encouraged parents to simply sign an exemption.
"One of the problems with the old law is it made convenience exemptions easier than finding your child's records," said Michele Roberts, a spokeswoman for the state Department of Health's immunization program.
In Washington, a parent's decision to exempt his or her child for one or more vaccines is allowed for medical, religious or personal reasons. Of the 6,878 students in Snohomish County with exemptions during the 2010-11 school year, nearly 90 percent were for personal reasons.
When schools and local public health agencies have taken an in-depth look at the exemptions on file, they've found some surprising results.
In some cases, between a third to a half of all parents simply signed exemptions instead of finding their child's immunization records, Roberts said. In many cases, the child had, in fact, received immunizations.
As the mother of a 2-year-old, Roberts said she understands parents' questions and concerns. Many of the diseases that children are immunized against haven't been seen by this generation of parents, she said. "You don't see it as an immediate threat to your child. The reason why they're gone is so many vaccines have been so successful, and so many people in our community are immunizing their children."
Ezra Eickmeyer, who lobbied against the new state bill on behalf of the National Vaccine Information Center, predicted it will create more political tension and conflict over vaccines between doctors and patients.
A recent survey showed that nearly a quarter of pediatricians said they would discontinue medical care for families who don't follow the recommended vaccination schedule, he said.
"More and more parents are asking questions about the growing number of recommended or mandatory vaccinations," Eickmeyer said.
Stephens said in his 26 years as a physician he has never seen a child have a reaction to an immunization more serious than sore arms and short-term fever.
"I think parents underestimate the severity of the disease and overestimate the severity of vaccination," he said.
Sharon Salyer:425-339-3486 or firstname.lastname@example.org
More on the law
Information on the new state law on what steps parents must take if they seek exemptions from one or more vaccines for their children can be found at the state Department of Health website: www.doh.wa.gov/cfh/Immunize/schools/exemption-info.htm
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