At age two, Barbara Loe Fisher’s oldest son came to the pediatrician for his DPT shot and something went terribly wrong. She watched, terrified, as his eyes rolled back into his head and his body went limp. He had temporary paralysis. But the long-term effects were the hardest—this precocious little boy forgot his ABCs and became learning-disabled for life.

Fisher channeled her emotions into action and started a group called the National Vaccine Information Center in Vienna, Va. Her son is now 29, and she continues to push for safer vaccines and additional options for parents who believe their children are more susceptible than others to risk.

Publicity about kids who react to shots—combined with fears of autism and mistrust of traditional medicine—has led to a backlash against childhood vaccines. If too many parents opt out, public health officials say, it could spawn a dangerous resurgence of disease. Currently, less than two percent of parents avoid vaccinations, according to the U.S. Centers for Disease Control, but the figure is higher in certain states. Measles, mumps, polio and whooping cough outbreaks have already spread through parts of Colorado and the Midwest.

New York pediatric nurse practitioner Mary Beth Petraco saw this trend take a turn for the worse when one of her friends decided to pass up the chicken pox vaccine. Instead, the friend took her young daughter to a chicken pox party.

This is happening around the country—when a child comes down with a case of chicken pox, the parents send word to others in the community. They let the children share sippy cups and lollipops to increase the odds that all the little partygoers will get chicken pox, too.

The wild strain of chicken pox does build stronger immunity than the vaccine, says Petraco, coordinator of child health for Suffolk County Department of Health Services. But, as her friend discovered, chicken pox can be unpredictable.

The little girl scratched a lesion on her neck and got an infection. The swelling was so bad, it blocked her windpipe and she couldn’t talk. The girl survived the ordeal, Petraco says, but her mother regretted taking her to the chicken pox party.

“Before the vaccine, chicken pox hospitalized a lot of kids. There will always be some that have serious consequences,” says CDC spokesperson Curtis Allen. “If you go to a chicken pox party, you’re gambling.”

The current generation of parents making the decisions about vaccines doesn’t remember polio and whooping cough outbreaks. The most vulnerable—newborns and the elderly—are not protected from these diseases. So an older kid could pass it on to a baby sister with disastrous results.

“Even if they don’t die from it, having whooping cough is like torture and it can go on for weeks,” says Pat Hood, immunization coordinator with the county health department in Boulder, Colo. Children’s faces turn colors as they struggle for breath, and they can break their ribs from the force of their coughs.

Whooping cough has been a problem in Boulder County (which has a lower vaccination rate than other parts of the state and nation), so public health officials are increasingly turning to graphic information to show people what happens when infectious diseases get out of control.

In a highly educated community like Boulder, or, say, the upper West Side of Manhattan, people feel that research is part of their job as parents. But they don’t always know how to analyze medical reports, says Chana Goussetis, a Boulder health department communications specialist.

Many parents are still under the impression that the MMR vaccine (measles, mumps, rubella) has mercury in it and causes autism. Concerns over autism and vaccines peaked with Dr. Andrew Wakefield’s study in the late 1990s. While Wakefield raised important issues, his research wasn’t very credible. “A study of twelve people is not a good study,” Goussetis explains.

Since then, companies have taken the mercury out of vaccines. Over the past eight years, a series of studies have found no proof that mercury causes autism. So why do people still think it does? “It’s part of the whole distrust of institutions that has become so much a part of our culture,” says Dr. Lou Cooper, a Columbia University pediatrician.

“It’s all about trust,” Cooper says. He admits physicians are too hurried, pushing parents out the door before they have a chance to ask questions. “We need to create a climate of candor, transparency and openness,” he says.

When Cooper helps parents decide about vaccinations, he does risk analysis. For example, he says, studies show the MMR vaccine is safe. On the other hand, if you do nothing, your child is 35 times more likely to contract measles. Though measles has become very rare in the U.S., it still causes a few deaths each year among children; globally about 300,000 a year die from measles.

Fisher argues there are still too many unknowns about the vaccines themselves. She believes any parent worried about genetic vulnerability should have the right to opt out. For example, she says, the number of childhood vaccines required by law has doubled over the past 25 years. Is the immune system built to handle 56 doses of 16 different vaccines? And children are getting four or more shots at a time—what about the synergistic effects?

“People are looking for something less invasive and less toxic,” Fisher says. “Should we be manipulating the immune system with drugs and vaccines? Or should we be enhancing the immune system and not be so afraid of getting sick?”