An unlikely issue — whether to vaccinate preadolescent girls against a sexually transmitted virus — has become the latest flashpoint among Republican presidential candidates as they vie for the support of social conservatives and Tea Party members.

The issue exploded Monday night when Representative Michele Bachmann and former Senator Rick Santorum attacked Gov. Rick Perry of Texas during a debate for issuing an executive order requiring sixth-grade girls to be vaccinated against the human papillomavirus, criticizing the order as an overreach of state power in a decision properly left to parents. Later, Sarah Palin, who has yet to announce her 2012 intentions, also found fault with Mr. Perry.

The issue pushes many buttons with conservatives: overreach of government in health care decisions, suspicion that sex education leads to promiscuity and even the belief — debunked by science — that childhood vaccinations may be linked to mental disorders.

On Tuesday, Mrs. Bachmann, of Minnesota, raised that concern by suggesting that Mr. Perry had put young girls at risk by forcing “an injection of what could potentially be a very dangerous drug.” Appearing on NBC’s “Today” show, she recounted that after the debate in Tampa, Fla., a tearful mother approached and said her daughter had suffered “mental retardation” after being vaccinated against HPV. “It can have very dangerous side effects,” Mrs. Bachmann said.