The controversy was ignited by Republican presidential hopeful Michele Bachmann, who claimed that the vaccine against human papillomavirus, which can cause cervical cancer, was a "very dangerous drug" that could lead to "mental retardation".
That claim immediately drew a barrage of criticism from the medical profession and even from Bachmann sympathisers on the right, forcing her to backtrack slightly. She told a conservative talkshow: "I have no idea. I am not a doctor, I'm not a scientist, I'm not a physician. All I was doing is reporting what this woman told me at the debate."
But doctors and scientists say that her remarks risk further reducing the already low take-up rates for the vaccine, as more parents will be convinced to reject the vaccine for their daughters.
Professor Gregory Zimet, co-leader of the cancer control programme at Indiana University, said of Bachmann's comments: "People will say there's no evidence for it and that is true, there is no evidence. But I would go further: Bachmann is absolutely wrong."
He added: "Part of the issue will be how long the discussion is prominent in the news. If this is brought up every time the Republican candidates have a debate, if misinformation is repeatedly expressed and covered nationally, it can have a negative effect."
The uptake of the vaccine has already suffered a major backlash in the US in response to what some critics viewed as an overly aggressive marketing strategy and anxiety from the religious right that the vaccine would promote sexual promiscuity among young girls.
The American Academy of Pediatrics, the Centers for Disease Control and Prevention and the American Academy of Family Physicians all recommend that girls receive the HPV vaccine at the of age 11 or 12, before they begin having sex.
According to the CDC, around 49% of girls aged 13 to 17 received one dose of the vaccine in 2010, but only 32% received all three doses.
"From the public health point of view that is inadequate," said Zimet. "When you have a vaccine that likely prevents around 70% of cervical cancers, but fewer than half of girls are receiving all three doses, the ultimate effect is dampened."
In the US, around 6m people a year become infected with HPV, and some 4000 women die of cervical cancer each year.
Bachmann had focused on the HPV virus to attack her rival in the Republican nomination race, Texas governor Rick Perry, over his decision to issue an executive order requiring girls in the state to have HPV vaccines. She also suggested that he may have made the order in return for political donations from Merck, the manufacturer of the Gardasil, the vaccine used in the US.
Both allegations drew political blood, and Perry found himself on the back foot before the otherwise largely supportive Tea Party audience suspicious of "big government" intrusion on individual liberties.
But Bachmann appears to have badly overplayed her hand by then telling NBC television: "I will tell you that I had a mother last night come up to me here in Tampa, Florida, after the debate. She told me that her little daughter took that vaccine, that injection, and she suffered from mental retardation thereafter," said Bachmann. "It can have very dangerous side effects."
Ed Rollins, Bachmann's former campaign manager, criticised her comments: "She made a mistake. The quicker she admits she made a mistake and moves on, the better she is," he said in an interview on MSNBC.
"Ms Bachmann's an emotional person who basically has great feeling for people. I think that's what she was trying to project. Obviously it would have been better if she had stayed on the issue," he said.
"I think the bottom line here is she has made what was a very positive debate and made the issue about Perry to where it's now an issue about her, and she needs to move on.''
Although offering the vaccine at such an early age is sometimes controversial, its effectiveness and safety have not been a political issue in the US.
Dr Marion Burton, the president of the American Academy of Pediatrics, hit back at Bachmann.
"The American Academy of Pediatrics would like to correct false statements made in the Republican presidential campaign that HPV vaccine is dangerous and can cause mental retardation. There is absolutely no scientific validity to this statement. Since the vaccine has been introduced, more than 35m doses have been administered, and it has an excellent safety record," Burton said.
The Institute of Medicine, which advises the government, last month found the HPV vaccine to be safe.
But while there is absolutely no evidence to suggest that the vaccine is dangerous, there are some questions over the efficacy of Gardasil, the version of the vaccine used in the US.
Clinical trials show that Gardasil is highly effective against two strains of the HPV virus that together account for around 70% of cervical cancers. The vaccine works best in young people who have never had an HPV infection.
In countries with popular cervical cancer screening programmes, vaccination with Gardasil can reduce the number of abnormal smear test results by around 20%.
"That means sparing women from the psychological trauma and gynaecological procedures that arise from an abnormal result," said Anne Szarewski, a cervical cancer expert at the medical charity Cancer Research UK.
But questions remain over the value of Gardasil in preventing cases of actual cervical cancer where cervical screening programmes are widely subscribed to, said Diane Harper, a Professor of Medicine at the University of Missouri in Kansas City, who led the clinical trials of Gardasil and its main competitor, Cevarix, manufactured by GSK.
Smear test programmes that look for precancerous changes to cells in the cervix caused by the virus have reduced the incidence of cervical cancer in the US to around eight in 100,000 women.
"The very best you could achieve with Gardasil alone would be 14 cases per 100,000 women. So in an overall population, Gardasil is never going to prevent more cervical cancers than you are already preventing with a screening programme," Harper told the Guardian.
Another concern centres on how long the vaccine lasts. If a woman who received the jab was protected for only five years, any infection and resulting cancer would only be delayed until the immunity wore off.
Gardasil targets two strains of the HPV vaccine, while Cevarix is designed to protect against five strains. Mathematical models of Cevarix suggest the vaccine should protect against the virus for 30 years.
Bachmann's claims also drew criticism on the right.
Yuval Levin, a former domestic policy advisor to George Bush's administration and former chief of staff of the President's Council on Bioethics, called Bachmann's assertions "preposterously ill-informed" and "profoundly irresponsible".
"Baseless assertions to the contrary about various vaccines have for years been piling needless guilt upon the parents of children with autism and other disorders, and driving other parents away from vaccinating their children against diseases that could do them great harm. A presidential candidate should not be engaging in such harmful nonsense," he said in the conservative National Review Online.
Even the popular rightwing radio talk show host, Rush Limbaugh, said that Bachmann "may have jumped the shark" – an idiom generally used to mean having gone too far – by linking the HPV vaccine to mental retardation.
Limbaugh said that Bachmann appeared undercut her initial success in wounding Perry over the HPV issue by shifting the focus to her own credibility with her claims about the vaccine's safety.
"She scored the points and should have left it there," said Limbaugh.
Chris McGreal and Ian Sample @'The Guardian'
