Vaccines have changed the world, largely eradicating a series of terrible diseases, from smallpox to polio to diphtheria, and likely adding decades to most of our life spans. But despite the gains -- and numerous scientific studies indicating vaccine safety -- a growing movement of parents remains fearful of vaccines. And in some American communities, significant numbers of parents have been rejecting vaccines altogether, raising new concerns about the return of vaccine-preventable diseases like measles and whooping cough.

Nowhere has this debate grown more heated than in Ashland, Ore. -- an area that FRONTLINE learns is of high concern to the Centers for Disease Control and Prevention. With an estimated quarter of the town's children entering kindergarten not fully immunized, Ashland is one of the least vaccinated places in America. Despite the best efforts of local pediatricians like Dr. Donna Bradshaw-Walters, many parents are simply not convinced that vaccines do more good than harm, and they've been using Oregon's religious and personal-belief exemption to get out of the state vaccine mandate. "I think a child's immune system is so immature," says Jennifer Margulis, an Ashland writer and mother of four. Margulis decided against following the recommended CDC schedule -- although prior to a trip to Africa she did have her children vaccinated for yellow fever, tetanus, polio and meningitis. Says Margulis, "If you read the list of ingredients about what you're putting intramuscularly into your child, it's scary."

In The Vaccine War, FRONTLINE lays bare the science of vaccine safety and examines the increasingly bitter debate among the public health establishment, doctors and a formidable populist coalition of parents, celebrities, politicians and activists determined to resist pressure from the medical and public health establishments to vaccinate, despite established scientific consensus about vaccine safety.

In this video excerpt from The Vaccine War, consider differing perspectives among doctors, parents and public health officials on the risks and benefits of vaccines:

Video Segment Themes:

• Vaccines have increased our lifespan by 30 years and have largely eradicated certain diseases, like smallpox and polio.
• While vaccination now prevents 16 different communicable diseases in the United States, some parents are concerned about the safety and sheer number of vaccines given to young children.
• While vaccination now prevents 16 different communicable diseases in the United States, some parents are concerned about the safety and sheer number of vaccines given to young children.
• The issue of vaccination can be contentious on both sides and involves balancing the risks to the public as a whole versus the risks to any one family or child.