As Nicole Matten spoke about the sudden death of her 7-year-old daughter, she clasped a large, framed portrait of the smiling girl and held back her tears.
"She was perfectly healthy," Matten told a crowd outside Vermont's Department of Public Health in March. Kaylynne, she said, was healthy, until she was given a routine flu shot at her pediatrician's office last December. She fell ill almost instantly, she said, and was dead within days.
Matten was one of a handful of Vermont residents to rally against a bill that would make vaccines mandatory for school-aged children by eliminating "philosophical exemption" as a reason to opt out of the shots.
"Now, while we're grieving for our beautiful 7-year-old Kaylynne, we have to worry about our philosophical exemption being taken away for our other kids," said Matten. "It should be a parent's choice, this should be a free country."
Around the same time, inside the walls of the state Senate, Kayla Thomas, 19, of Rutland, Vt., emotionally described losing her 2-year-old brother to meningitis more than a decade ago. Now there is a vaccine available to prevent that illness.
"If the shot was around then he would still be here," Thomas said, in her testimony in support of vaccinations.
The debate over the bill has divided Vermont's families over the benefits and risks of vaccines. It has also pitted the state House-- whose majority voted down the bill -- against the state Senate, which voted to approve it.
Twenty states, including Vermont, currently allow philosophical exemptions for those who object to vaccines for personal or moral reasons.
"It's been clearly demonstrated that the broader (the) exemptions, the more loosely it's applied -- and the less likely children will get vaccinated," said Dr. William Schaffner, chair of preventive medicine at Vanderbilt University School of Medicine in Nashville, Tenn.
Fewer than 70 percent of children in Vermont between the ages of 18 months and 3 years received all of the recommended vaccines, according to a 2010 National Immunization Survey by the Centers for Disease Control and Prevention -- a rate lower than the 73 percent national average. Vermont has one of the highest philosophical exemption rates among those 20 states, Dr. Harry Chen, health commissioner for Vermont's Department of Public Health, told ABC News.
Measles and pertussis, also known as whooping cough, are the fastest growing vaccine-preventable diseases nationwide. Just last year, Vermont had an outbreak of pertussis. And other states with high philosophical exemption rates, including Washington and Oregon, have also seen a revival of pertussis.
According to the Vermont Coalition for Vaccine Choice, an advocacy group of parents, health care providers and others lobbying to stop the bill from passing, many people are naturally immune to communicable diseases without the need for vaccines.
The group also maintains that mass vaccinations will lower the risk of infection among people who decline the vaccinations, a phenomenon known as "herd immunity."
"There is no need to allow the state to strip parents of their rights to make medical decisions for their own kids," the group's website reads. "Given that vaccines have known risks associated with them, it seems only prudent to continue the philosophical exemption, and to make sure that we are not divided by fear mongering."
Calls to the Vermont Coalition for Vaccine choice were not immediately returned.
Schaffner said it's impossible to know who would have natural immunity, adding that herd immunity works only if the majority of the population is vaccinated, which stresses the importance of getting vaccinated.
"Parents who withhold their own children from immunization are taking advantage of all those who do get their children immunized," he said.
In addition, he said, some children have medical conditions that preclude them from receiving vaccinations.
"The way we protect them is for all the rest of us to be protected," Schaffner said.
Given the current resistance to Vermont's bill, passage is expected to be a hard fought battle.
The bill is now being discussed in a conference committee, which consists of three house and three senate members, to negotiate the terms of the bill. The committee has already met three times and is scheduled to decide by the first week of May.
"The realistic expectation is that a compromise will be struck and that will make philosophical exemptions harder to attain," he said.
Amy Pisani, executive director of Every Child by Two, an organization that advocates for vaccinations, said such a compromise should require that parents receive education on the importance of vaccines.
"The question at hand is whether individuals have the right to shirk the laws put in place to maintain the health of some of Vermont's most vulnerable citizens; infants and school children," she said.