Carly Fiorina speaks at the Iowa Faith and Freedom Coalition's forum in Waukee, Iowa, in April. (REUTERS/Jim Young)

ALDEN, Iowa -- GOP presidential hopeful Carly Fiorina said Thursday that parents should not be forced to vaccinate their children against diseases like measles and mumps, although she added that public school systems can forbid unvaccinated children from attending.

"When in doubt, it is always the parent's choice," Fiorina said during a town hall in an agricultural building in rural Iowa on Thursday evening. "When in doubt, it must always be the parent's choice."

Fiorina's comment came in response to a question from a mother of five children who said that because of her religious beliefs, she will not allow her children to receive any vaccines that were created using cells from "aborted babies." Fiorina told the woman that parents must be allowed to make such decisions.

"We must protect religious liberty and someone's ability to practice their religion," said Fiorina, receiving a round of applause. "We must devote energy and resources to doing so. Period."

Fiorina, the former CEO of Hewlett-Packard who has never held elected office, recounted a discussion she had with her daughter, who was hesitant to have her own daughter vaccinated against the sexually transmitted disease HPV.

"And she got bullied. She got bullied by a school nurse saying: 'Do you know what your daughter is doing?'" Fiorina said. She said her daughter's response was this: "Yes. I do, actually."

After the town hall, Fiorina further explained her stance on vaccinations to a group of reporters: "When you have highly communicable diseases where we have a vaccine that's proven, like measles or mumps, then I think a parent can make that choice -- but then I think a school district is well within their rights to say: 'I'm sorry, your child cannot then attend public school.' So a parent has to make that trade-off."

Fiorina said that when it comes to "these more esoteric immunizations" for diseases that are not contagious or communicable, school districts should not be allowed to mandate that children receive the vaccination.