Oct. 31, 2008 -- A prominent infectious disease specialist's accounts of death threats he received from vaccine opponents exposes a kind of harassment in connection to fears of a link between vaccinations and autism, vaccine researchers say.

Dr. Paul Offit, medical director of the Vaccine Education Center at The Children's Hospital of Philadelphia and a vaccination proponent, recounted his experiences to Dr. Nancy Snyderman Thursday morning on NBC's "Today" show.

Snyderman said on the program that the threats Offit received included a "phone call from an unidentified man who mentioned specific and private details" about Offit's family.

"And then he hung up," Offit said. "But the implication was clear -- he knew where my children went to school."

Dr. Gregory Poland, director of the Mayo Vaccine Research Group at the Mayo Clinic in Rochester, Minn., and a vocal proponent of universal flu vaccination, says he is no stranger to such harassment.

"Among the most egregious things -- I got a letter once railing against my involvement in vaccines and hoping that something serious would happen to me and hoping that something serious would happen to one of my children," he said. "I had people come to the door of my home and harass my wife and kids, so I no longer have my address listed in the phone book."

And at one point, Poland said, someone broke into his lab and attempted to hack into his computers. As a result, Poland's lab is now locked down for security purposes.

But some people connected to groups that believe a vaccine-autism link exists say that they, too, have been the targets of hateful speech.

"I've been called a baby killer," says Rebecca Estepp, national manager of the autism support group Talk About Curing Autism. "One woman got into my face this summer and told me I was going to cause millions of children to die. Emotions are running high because this involves the health of our children.

"Nancy Snyderman and Paul Offit are carrying on about it, but it happens to us, too. I have sympathy because I know exactly how it feels."

While researchers note that the overwhelming weight of the scientific evidence exonerates vaccines as a cause of autism, some groups still believe that the shots children receive when young are somehow tied to the condition.

But if the vitriol on both sides has proven one thing, it is that the issue is no longer about the science alone.

Michael John Carley, author and executive director of the Global and Regional Asperger Syndrome Partnership Inc. (GRASP), has himself been diagnosed with Asperger syndrome, a condition on the autism spectrum. In his upcoming manuscript entitled "Cures, Vaccines, Research, and the Promise of Alarmist Rhetoric: Autism Politics 101," Carley notes that for some, the fears about unvaccinated children or widespread autism have taken secondary importance.

"[W]hat has dwarfed these doomsday scenarios is the vitriolic nature in which the argument has descended," he wrote. "The shameful tactics, hurtful statements and outright mismanagement conducted by both sides has made the 'cure' debate look like a friendly disagreement by comparison."

Carley, too, has experienced backlash from some of this anger for his view that no link exists between vaccines and autism. He says that he has personally received "tons of hate mail," although he has not yet received a death threat.

Threats Emerge From a Minority

Estepp, the autism support group manager whose husband is in law enforcement, said everyone with whom she is involved would condemn the harassment that Offit has endured.

"No one should ever receive death threats," she said. "No one should ever know where his children are. That's horrible, and I'm sorry to hear that is happening."

Estepp said she believes that those who engage in such threats represent only a small portion of the overall community, a point with which the pro-vaccination Offit agreed.

"In any movement you have some fringe people who are very passionate and make some wrong choices," Estepp said, adding that reports of such threats against vaccine proponents are damaging to groups such as hers.

They unfairly paint those on her side of the debate as irrational and potentially violent, she said.

And Offit said the anger that some parents experience is understandable. "For parents of children with autism, it's really hard," he says. "It's emotionally hard, it's financially hard.

"When there's the notion that there's something to blame, you can see where the anger would come from."

But even if the threats are emerging from a small section of those who oppose recommended vaccine schedules, those in the field say that they have a definite impact on the work they do.

"Does it stop me from speaking what I think is the truth? No," Poland said.

But, he notes, "I know of colleagues who have decided to write something slightly different or say something slightly different because they are afraid of inciting anti-vaccine groups."

Dr. William Schaffner, professor and chairman of the Department of Preventive Medicine at the Vanderbilt University School of Medicine in Nashville, Tenn., said, "The threats certainly -- as well as the anticipation of heated 'feedback' -- clearly has inhibited colleagues from engaging in the public discussion of contentious issues regarding vaccines, Lyme disease, etc."

Schaffner said he has never received such threats. But, he added, "as to myself, this unpleasantness makes me very wary; we are a society that is prone to violence."

Poland said he believes legislation should be considered to offer special protection to those in the field of vaccine research.

"Since this affects not only a person and his or her family, but indeed the public health, special provisions should be considered in terms of legal consequences," he said. "This was done, for example, in the case of abortion protesters."

What Should Be Done?

But are such steps necessary? Thus far, no one has followed through with threats made against those in the field of vaccine research; likewise, there has been no report of any violence being visited on those in the autism community for their views.

Still, all involved say something should be done to help defuse the personal side of the debate.

Dr. Peter Hotez, immunologist at George Washington University in Washington, D.C., and father of a daughter with autism, said he believes that federal public health agencies, including the surgeon general's office and the National Institutes of Health, must take a more active role in dissuading the link between vaccines and autism.

"[These organizations] have to be willing to speak out and make strong statements that vaccines do not cause autism," he said. "These organizations have been conspicuous by their silence."

Meanwhile, the escalating tension has Poland worried about the potential for violence.

"These things, they bother you because the nature of violence is that it's unpredictable," he said. "Does it take a personal injury, a death or property damage before something is done?"

Kirk Fernandes and Audrey Grayson contributed to this report.