COLUMBIA — Gov. Nikki Haley has vetoed a bill that could have allowed seventh-grade students to get a free vaccination against a sexually transmitted virus that can cause cancer in women.

Haley once supported an effort to require the vaccinations for middle-schoolers, leading critics to blast the veto as hypocritical.

Haley said the bill was unnecessary because its language would merely allow, not require, the S.C. Department of Health and Environmental Control to implement a voluntary vaccination and education program on human papillomavirus, or HPV.

And the measure by Rep. Bakari Sellers, D-Bamberg, is a precursor to “another taxpayer funded healthcare mandate,” the governor said in her veto message.

The bill's vaccination program would have been contingent on receiving state and federal funding.

Sellers and a reproductive-health advocacy group said Haley put politics over women's health.

“This is a common-sense approach to a very serious problem,” Sellers said. “To call this measure unnecessary is demeaning and insulting to the heroic women who fight this cancer every day.”

While a Republican House member representing Lexington County in 2007, Haley co-sponsored a bill that would have made HPV vaccination mandatory for girls entering seventh grade.

She said on her gubernatorial campaign website two years ago that she ultimately voted to kill the bill because it would not have allowed parents to opt their daughters out of the program.

But during the debate on the 2007 bill, Haley voted to kill an amendment that would have added the opt-out option.

On Tuesday, she described her co-sponsorship of the bill as a mistake.

Haley, the mother of a 14-year-old daughter, said parents should have the right to decide whether their daughters receive the vaccination.

But an S.C. reproductive-health advocacy group called Tell Them said Haley's shift shows that her veto was politically motivated and not in the best interest of the state's young adults.

The Legislature could override Haley's veto with a two-thirds vote of both chambers.

HPV is the most common sexually transmitted infection, according to the Centers for Disease Control and Prevention.

About 20 million Americans currently are infected by HPV, and it leads to cervical cancer in about 12,000 American women annually, according to the CDC.

The National Cancer Institute has ranked South Carolina ninth in the nation for estimated deaths from cervical cancer.

On infected skin, HPV can cause normal cells to turn abnormal, according to the CDC. After becoming infected, patients might develop warts within weeks or months. Cancer could take years to develop.

Dr. Ashlyn Savage, an assistant professor of obstetrics and gynecology at the Medical University of South Carolina, recommends the HPV vaccine for all patients, boys and girls.

“There's a significant benefit, and the harms are very small,” Savage said of the vaccine, administered in a three-shot series. “I universally recommend it to all patients.”

The vaccine protects girls older than 9 against cervical cancer, according to DHEC. Boys older than 9 also can receive the vaccine to help protect against genital warts, according to DHEC, which recommends the vaccination before becoming sexually active.

Savage called cervical cancer a “disease of under-served women” who are not screened regularly at check-ups. She said a school-based vaccine would “allow a large volume of young girls to receive it.”

Dr. Colleen Boylston of Trident Health System said the vaccine should be administered in a physician's office rather than at school.

“I think education needs to be provided, and materials sent home from school would be appropriate,” Boylston said.

Sellers' bill would have allowed schools to provide informational brochures on the vaccine to parents of sixth-graders.