The scientific community is confounded by the lingering vaccination fear.
Some public health officials seem eager to ignore the issue and believe vaccine critics have received too much attention. They point to the overwhelming research showing vaccines are not the cause of increasing autism rates and hope that's enough to convince doubters.
Other health authorities continue to speak out in an attempt to reassure nervous parents.
"Vaccines are the safest way to prevent disease," said Wash. State Health Secretary John Wiesman. "We know that vaccines save lives."
In the wake of mounting evidence, the scientific debate regarding vaccinations has ceased but public fear remains.
Washington continues to lag behind the country in immunization rates, despite a 2011 modification in state law wisethat requires parents seeking a personal/philosophical exemption for their children to first speak with their health care providers.
Analyzing the state immunization data from reporting school districts across Washington, KIRO 7 found the districts that have the highest personal exemption rates.
We focused our attention on districts with 25 or more kindergarteners and a philosophical exemption rate higher than the statewide average of 3 percent.
The district with the highest personal exemption rate is Orchard Prairie, in Spokane, with 24 percent. The second highest personal exemption rate is Vashon Island with 17 percent.
Rates in Seattle and Spokane schools are in line with the statewide average while Tacoma has a higher immunization percentage; parents there opt out just 1.3 percent of the time for philosophical reasons.
Click here to see a breakdown immunization opt-outs by Washington school districts.
The largest, most rigorous and replicated studies all show vaccines are not behind the growing number of autism diagnoses around the world.
So, why isn't logic enough?
Maybe it's because the other side has something more emotionally powerful—families who are convinced their children became autistic after receiving vaccinations.
Actress, Playboy model and current co-host on The View, Jenny McCarthy exemplifies the compelling nature of the movement.
She believes her son's autism was caused by the measles, mumps and rubella vaccine; she co-wrote a book about how she cured him by using various therapies and diet changes.
McCarthy has been at the forefront of the anti-vaccine effort, warning parents to delay or eliminate the number of vaccines their children receive.
She and others are so persuasive scientists have researched their concerns.
Vaccine critics' arguments have subtly shifted through the years.
First they were alarmed about Thimerosal, a type of mercury used to preserve vaccines since the 1930s.
Because of the well-documented concerns about mercury and children, as a precaution, Thimerosal was removed or reduced to trace amounts in all regularly recommended vaccines for children six and under back in 2001.
The acceptable trace amount is one microgram or less. For perspective, an eyelash weighs about 75 micrograms.
Only the flu vaccine has more Thimerosal but it can be specially ordered to also have only a trace of the preservative.
Since Thimerosal has been removed or reduced from childhood vaccines there has not been a decline in the rates of Autism Spectrum Disorder in the U.S. In fact, the diagnosis continued to rise; one in 88 children has ASD.
Vaccine critics then shifted their attention to other additives like aluminum and formaldehyde.
Scientists say they're necessary to make vaccines effective and protect against bacteria.
They point out the amount of aluminum in vaccines is a thousand times less than an antacid tablet. And most formaldehyde is removed from vaccines before it's packaged.
If it's not additives, is there a specific problem about the measles, mumps and rubella vaccine?
For that, we go to Japan, where MMR immunization plummeted in the 90s after the Urabe strain used to make the mumps component of the Japanese MMR vaccine was linked to a less than one percent increase in Aseptic meningitis. (The Urabe strain was never used to make the MMR vaccine in the U.S.)
People who contract mumps naturally will also develop Aseptic meningitis 10 percent to 15 percent of the time. Though the meningitis risk with the Urabe strain was a fraction of the risk associated with natural mumps, it was discontinued and replaced.
But by 1993 few Japanese got the MMR shot despite the change.
Since then Japan has been called an exporter of measles and there's a current CDC travel warning to the country because of a rubella outbreak.
The increasing interconnectivity of our world means disease outbreaks put everybody at risk.
"You don't have to travel to be exposed to disease with this type of reverberation and waves, it can travel here to us," said Dr. Jane Dimer, Group Health OBGYN. "A virus or some bacterial infection can travel the world in 24 hours these days."
The unique circumstances in Japan made it possible for scientists to study on a large scale what happens to autism rates when MMR immunizations plummet.
The results were published in the Journal of Child Psychology and Psychiatry in 2005; researchers found ASD rates "rose dramatically" after MMR immunization dropped, ruling out a link between the two.
Many vaccine critics opt out or delay because they worry the CDC's 11 recommended immunizations before 2 years old are "too many, too soon."
So, researchers studied that as well. The results were published in the Journal of Pediatrics just this year.
The finding: Multiple vaccines to children before they turn 2 doesn't increase their risk of autism.
Experts warn opting out and delaying vaccines does have consequences. Diseases we'd come close to eradicating in the U.S. are making a comeback.
We're on pace for the worst measles outbreak in nearly 20 years.
Last year, our state saw an epidemic of whooping cough with more than 5,000 cases.
The resurgence of pertussis or whooping cough is partly attributed to pockets of unvaccinated children.
The disease is highly contagious and can be life-threatening for babies.
"People think their kids will get it and they'll just have a little cough, no big deal," Michelle Razore said.
Razore's daughter, Natalie Razore, caught whooping cough when she was 2 weeks old.
"The first three weeks we would just watch her hours upon hours just gasping for air, wondering if she would ever take another breath," said Razore.
Natalie Razore spent months at Children's Hospital while coughing fits robbed her of oxygen, causing her body to shut down. She endured two full-body blood transfusions,and survived a blood infection and a blood clot in her leg that nearly resulted in amputation.
Today, Natalie Razore is a vibrant 3-year-old -- but there are still lasting effects from whooping cough.
"This is something we'll be dealing with for the rest of her childhood and I'm sure she'll be dealing with it for the rest of her life," said Razore.
The blood clot damaged Natalie Razore's left leg so badly it isn't growing properly and she's forced to walk on the ball of her left foot. Doctors in Seattle again recommended amputating Natalie's leg when she was about 2 years old.
Razore is thankful she and her husband, Joe Razore, have the means to get treatment from the only doctor in the country who specializes in Natalie Razore's leg injury.
"Luckily we found a doctor who specializes in Minnesota, so we're travelling every six months to Minnesota. She'll be having surgery every couple of years and will be in a wheelchair [for six months] after every single [surgery]," said Razore.
To this day, no one knows how Natalie Razore contracted whooping cough.
"It could've been in the hospital when she was born, it could've been in the grocery store," Razore said.
Experts said most babies get pertussis from their moms or other family members, which can have a devastating impact.
"A kiss is a kiss but it can be an infection," Dimer said.
That's why Dimer urges all adults and children get their recommended DTap and TDap boosters.
She thinks immunizations are so important she keeps her children's vaccine schedule in a special space at home.
"I put it on the garage wall. It's right next to the soccer and lacrosse schedule."
Because infants under 2 months old and other vulnerable groups can't get the pertussis vaccine, they must rely on other people receiving vaccinations to contain the disease in communities.
Razore hopes Natalie Razore's story reminds people why vaccines were first created and why they're still necessary.
Links to research used in this story
Special thanks to Dr. Jeff Duchin, Chief of Epidemiology King County Public Health.