Yet according to a new study by Harvard University researchers, Meeks’s pledge to remain a virgin until he is married has a less than 50% chance of success. The researchers claim that the well-meaning commitment tends to wear off within a year.

The study has sparked fresh controversy over a US government-funded drive to persuade teenagers to abstain from sex. Critics claim that President George W Bush is pandering to religious conservatives by spending $178m (£96m) this year on abstinence programmes that a series of studies have shown to be of limited effect.

The row has overshadowed a breakthrough in combating sexually transmitted diseases (STDs). The development of a new vaccine that protects women against viruses linked to cervical cancer has upset some parents who fear that the campaign will be undermined if girls are led to believe that a vaccine will protect them.

The latest developments follow a series of setbacks for the abstinence movement which once claimed Britney Spears as a virginal role model. The singer later confessed that she had broken her vows with the pop star Justin Timberlake.

Despite conservative claims that the campaign has been responsible for a striking drop in teenage pregnancies over the past 15 years, one study found last year that teenagers who make abstinence pledges have the same rate of STDs as those who do not take vows.

Hannah Bruckman and Peter Bearman found in a study published in The Journal of Adolescent Health that teenagers committed to abstinence tended to delay vaginal intercourse, but were still likely to engage in other forms of sexual activity. Researchers argue that those who have taken the pledge are more likely to engage in unprotected sex if they forget their vows in the heat of passion.

The Harvard study, to be published in next month’s issue of the American Journal of Public Health, was based on a survey of 13,000 teenagers. Janet Rosenbaum, a Harvard researcher, found 53% of adolescents who made a pledge changed their mind within a year.

The latest study angered campaigners, who dismissed the findings as “junk science” and “politically motivated”.

“I don’t buy it,” said Janice Crouse of the Concerned Women for America, a conservative pressure group. “The hard data is that teen pregnancies are down. Abortions are down.”

US government statistics indicate that abortions fell from 42 teenagers per 1,000 women in 1986 to only 16 by 2002.

But many teachers and social scientists argue that the fall was due to improved sex education, wider availability of condoms and the pill and greater access to sexual information online.

Yet the effect of all that “sex ed”, argued Keith Deltano, a former teacher who tours schools advocating abstinence, is that the average American is exposed to between 240,000 and 480,000 sex acts before reaching the age of 18.

He claimed America is in the throes of a “new sexual revolution — and those choosing not to have sex are the true rebels”.

The fallout from the controversy has proved to be a headache for one of the world’s biggest pharmaceutical companies. Earlier this month a federal health panel gave a preliminary green light to Gardasil, a vaccine developed by Merck. It has been shown to protect against two types of human papilloma virus, which is mostly spread by sexual contact and is the cause of about 70% of cervical cancers.

Medical experts believe the drug will work best if given to girls and young women before they become sexually active.

Many conservatives recognise that battling a life-saving medical advance would be political suicide. But die-hards remain suspicious. “Premarital sex is dangerous,” wrote one on the Abstinence Clearinghouse website. “Let’s not encourage it by vaccinating 10-year-olds so they think they are safe.”

Explore World News

• Iraq News

• US & Americas News

• Europe News

• Middle East News

• Asia News

• Africa News

• Ireland News

Times Recommends

• Obama: the world can expect better of America
• Gulp! Mystery killer threatens French oyster
• Secret of Northn Lights key to space safety