During a debate last week for Republican presidential candidates and in interviews after it, Representative Michele Bachmann called the vaccine to prevent cervical cancer “dangerous.” Medical experts fired back quickly. Her statements were false, they said, emphasizing that the vaccine is safe and can save lives. Mrs. Bachmann was soon on the defensive, acknowledging that she was not a doctor or a scientist.

But the harm to public health may have already been done. When politicians or celebrities raise alarms about vaccines, even false alarms, vaccination rates drop.

“These things always set you back about three years, which is exactly what we can’t afford,” said Dr. Rodney E. Willoughby, a professor of pediatrics at the Medical College of Wisconsin and a member of the committee on infectious diseases of the American Academy of Pediatrics. The academy favors use of the vaccine, as do other medical groups and the Centers for Disease Control and Prevention.

The vaccine, recommended by the medical groups for 11- and 12-year-olds, protects against the human papillomavirus, or HPV, a sexually transmitted infection that can cause cancer. Use of the vaccine was disturbingly low even before the Bachmann flap, health officials say. That is partly because of the recent climate of fear about vaccines in general, and partly because some parents feel that giving the vaccine somehow implies that they are accepting or even condoning the idea that their young daughters will soon start having sex.