"The old (whooping cough) vaccine was probably our most reactogenic vaccine, which is to say that it had the highest rate of side effects," says Offit. "I mean, it could cause seizures with fever -- although it didn't cause epilepsy, meaning the permanent seizures --[but] it certainly could trigger seizures it caused pain and tenderness at the site of injection it caused floppy baby syndrome, a so-called 'hypo-tonic, hypo-response' syndrome. It caused persistent, inconsolable crying. And so, there was always an interest in trying to make that vaccine safer. But the science had to catch up to that."
Those serious side effects were temporary, not the permanent conditions for which lawyers often sued vaccine makers. In fact, comprehensive studies also reviewed by the National Academy of Sciences did not find that the old vaccine caused SIDS or permanent brain damage.
Lost in this debate is the disease the vaccine prevents. Whooping cough racks a baby's body with violent fits of coughing. In its most extreme form, it kills. But after "20/20'"s vaccine report, many parents told their doctors, "I'm scared of your vaccine."
I asked Dr. Richard Saphir, my children's pediatrician, what he thought of that program.
"It was certainly alarmist," he said.
In fact, when my daughter Lauren got a fever after one of the vaccines, he decided not to give her the final shot, and a short time afterward, she got whooping cough.
Dr. Saphir said that the fact that I was a "20/20" correspondent made him even more anxious about giving my daughter the vaccine.
My daughter recovered from her whooping cough. She was surprised to hear that our reporting could confuse parents and influence doctors.
"Parents go in and force their physicians to agree to not give the vaccines even though the physicians say, you're making a stupid decision?" she asked. "Then you guys are doing a really bad thing."
Parent Suzanne Walther agrees. On internet sites, Walther read so many horror stories about vaccines, that so she postponed vaccinating her daughter, Mary Catherine.
"Some of the vaccine stories said that if I had my child vaccinated they were going to die of SIDS," she said. "I'm very protective of my children, I don't want to do something to them that might cause them harm."
But not vaccinating caused harm. Mary Catherine got very sick with spinal meningitis.
"Our pediatrician put us in an ambulance to go to Vanderbilt Hospital immediately," said Walther. "It is a deadly disease. There's a huge risk of deafness, blindness, it's very painful."
Mary Catherine recovered, but she's one of many kids who are coming down with diseases doctors once thought were nearly eradicated, like mumps, measles, and whooping cough.
These diseases are coming back because pockets of frightened parents won't vaccinate their kids, some, after they search for information and end up on websites like Barbara Loe Fisher's. I asked Fisher about how sites like hers scare parents.
"You're really the vaccines' scare center. When you scare people stupid, and they don't get vaccinated, that spreads nasty diseases," I said.
"I don't think I've scared anybody stupid. We do not tell people to vaccinate or not vaccinate," she replied.
Fisher says she can't say whether vaccines are "good or bad."
"You can't say vaccines are good, vaccines haven't done more good than harm?" I asked?
"It's a complex issue," she said.