Kristen O'Meara chose not to vaccinate her young daughters because she was a big believer in anti-vaccination research. That changed when all three were stricken with a case of rotavirus, which causes acute stomach distress.

"It was awful, and it didn't have to happen, because I could have had them vaccinated. I felt guilty. I felt really guilty," she told ABC News.



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O'Meara and her husband also fell ill.

A teacher living outside Chicago, she added that she had "scoured everything" about why vaccines might be harmful and had become "pretty convinced." She chose not to vaccinate based on the results of her research but had read only material that cast doubt.

"I put my kids at risk," she said. "I wish that I had taken more time to research from both sides before my children were born."

Her three children — all under the age of 7 — are now fully vaccinated, after an aggressive regimen to bring them up to date on recommended shots.

The American Academy of Pediatrics recommends vaccinations for practically every child, but in a study published last month the group says the number of parents who are refusing to vaccinate their children appears to be on the rise. In 2013, 87 percent of pediatricians surveyed had encountered patients who refused a vaccine for their child, up from 75 percent in 2006, according to their research

Among the most common reasons cited by parents for their refusal to vaccinate their children was their belief that vaccinations are unnecessary, the report said. Parents also cited a purported link between vaccinations and autism — a link that has been repeatedly disproved because the research it was based on was proved fraudulent.

The U.S. Centers for Disease Control and Prevention, 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 from diseases such as measles, mumps and chicken pox not only to protect individuals but also to confer herd immunity on communities.

After her frightening wake-up call, O'Meara is encouraging others to vaccinate their children.

"I'm here because I wanted to share my personal story ... and if it does help someone change their mind, then that's great," she said.