Mom Whose Child Died After Catching Chicken Pox Advocates for Vaccines Shannon Duffy Peterson said pediatrician talked her out of vaccinating child.

April 15, 2014 -- Abby Peterson was just a few weeks shy of her sixth birthday in 2001 when she caught a severe case of chicken pox that made her so weak that she came down with pneumonia, her mother recalled. Her little body couldn’t fight against two infections and after ten agonizing hours in the hospital, she died in her mother’s arms.

Both chicken pox and pneumonia are preventable with vaccines, but Abby’s mom, Shannon Duffy Peterson, who lives in the rural area of Sleepy Eye, Minn., said her pediatrician steered her away from vaccinating her daughter.

Vaccine Hesitancy Tweet Chat Today at 1 p.m. ET

“I asked for them and my doctor talked me out of it,” Duffy Peterson recalled. “He said vaccines were too new and recommended I expose my children to diseases instead because he felt they could build up their immunity naturally.”

Duffy Peterson said that she wishes she had questioned the doctor’s recommendations more forcefully. It was only discovered after an autopsy that Abby was born without a spleen, an organ that is an essential part of the immune system. This made her especially vulnerable to germs and viruses, Duffy Peterson said.

Since Abby’s death, Duffy Peterson has become a pro-vaccine crusader, speaking before the Minnesota legislature and helping to pass laws requiring childhood immunization in the state. She said that the small but vocal minority of parents who refuse to vaccinate their children for fear of adverse reactions including autism are well-intentioned but irresponsible.

“Not vaccinating is not taking full medical care of your child,” she said.

Most of the medical establishment agrees completely with Duffy Peterson. The U.S. Centers for Disease Control, the World Health Organization and dozens of other public health groups have stressed for years that vaccines are safe and necessary. They also say that the large majority of children must be immunized to protect both individuals and whole communities with so-called “herd immunity” from diseases such as measles, mumps and chicken pox.

“From a scientific point of view this is a closed question,” said Dr. William Schaffner, a professor at the Vanderbilt University School of Medicine in Nashville, Tenn. “Vaccines have virtually wiped out a number of diseases that used to plague this country –- and they do not cause autism.”

Some parents understand the importance of vaccines but are still fearful they may cause harm to a child’s developing immune system. In a recent essay for the Chicago Sun-Times, actress Jenny McCarthy questioned whether a delayed vaccination schedule would be advisable for some children, saying she has never been “anti-vax” but that she does believe that there is a gray area when it comes to the current vaccination schedule laid out by the CDC.

“My beautiful son, Evan, inspired this mother to question the 'one size fits all' philosophy of the recommended vaccine schedule,” McCarthy wrote in her essay. "This is an extremely important discussion and I am dumbfounded that these conversations are discounted and negated because the answers are not black or white. ... God help us all if gray is no longer an option."

But Schaffner said creating worry over the recommended immunization schedule -- up to 24 shots by the age of 2 and up to five pokes per visit -- is misleading and unfounded.

“The area is not gray. There is no injury to children getting vaccinations simultaneously. A child’s immune system is more capable, powerful and flexible than you would think it is,” Schaffner said.

Through a spokeswoman, McCarthy said had no further comment and asked that the Sun-Times piece speak for itself.

Related: Vaccinations? Let's Talk

Schaffner said that altering the timing of vaccines may seem like a compromise but it still poses a serious health risk because a child remains susceptible to vaccine preventable illnesses for longer periods of time. He said it also puts others, including people with compromised immunity and even fully vaccinated individuals, at risk by exposing communities at large to preventable diseases. And, he said, delaying vaccinations is more costly and makes it more likely a child never completes the full schedule necessary for protection against disease.

Related: Kristin Cavallari Defends Her Anti-Vaccine Stance for Her Children

“Vaccines spread out are often vaccines not received,” he said.

Duffy Peterson said she is sure all parents have their children’s best interest at heart but they have to follow the science and make educated choices when it comes to vaccines.

“Not vaccinating can kill your child,” she said. “No one wants to have a child die in their arms when it could have been prevented.”

Vaccine Hesitancy Tweet Chat Today at 1 p.m. ET

Nearly 8 percent of parents in a 2011 national survey refused to have their children immunized for personal, religious or medical reasons. Another 25 percent delayed their child’s vaccinations, citing safety concerns.

What’s your opinion on childhood vaccination? Do you think they’re harmful or that it’s harmful to delay or refuse them? Come share your thoughts on today’s ABC News Health tweet chat today at 1 p.m. ET. Moderator Dr. Richard Besser, ABC News’ chief health and medical correspondent will host the conversation. He’ll be joined by various public health experts, advocates and concerned parents.

Tweeting with us is easy. Here’s how.