More than 500 cases of mostly minor side-effects have been reported in girls and women who got the new cervical cancer vaccine, but U.S. government health officials say no additional warning labels are needed.

Many of the reports involved fainting, but teens tend to faint from vaccinations anyway, health experts said, and the number of cases doesn't exceed what was expected.

"There is absolutely no reason to think that there is anything in this vaccine, as opposed to another vaccine, that's going to make people more likely to faint," said Dr. John Iskander, of the immunization safety office with the U.S. Centers for Disease Control and Prevention.

At issue is Gardasil, a three-dose vaccine by Merck & Co. approved by the government last June for females ages nine to 26. The vaccine protects against strains of the human papilloma virus, or HPV, which causes cervical, vulvar and vaginal cancers and genital warts.

CDC officials on Thursday plan to present data at a scientific meeting in Atlanta about side-effects in girls and young women who got the shot. Health officials estimate that hundreds of thousands have received at least one Gardasil shot in the time period being studied, but they don't have an exact count, so it was hard to assess the significance of 500-plus side-effect reports.

No deaths, serious injuries reported

According to an advance report shared with the Associated Press, there have been 542 adverse health complaints. Injection site soreness was reported by nearly 20 per cent, fainting or dizziness was reported by 11 per cent and fever or nausea was reported in nine per cent.

None of the girls or women who fainted had a serious injury from falling unconscious and there were no deaths. However, health officials recommend a 15-minute waiting period after the shot before leaving the doctor's office, in case of fainting or other problems.

Health officials have been cautiously watching for reports of Guillain-Barre syndrome, a paralyzing side effect that has been associated with a few other vaccines. In the reporting period, there were three such cases.

"Based on these numbers, it's not worrisome to us that there's any sort of association between the vaccine" and Guillain-Barre, Iskander said.

On Wednesday, a Virginia-based advocacy group, the National Vaccine Information Center, which focuses on the risks of immunizations, put out a press release warning of Gardasil side-effects. The group said health officials did not do enough research into whether the vaccine leads to harmful problems when combined with other shots.

No evidence

But Iskander said there's no evidence Gardasil is harmful in combination with other vaccines.

The advocacy group also questioned a movement by some state legislatures to order the vaccine be given to all girls.

"We just don't know enough to be mandating Gardasil for anyone, much less vulnerable 11- to 12-year-old girls entering puberty," said Barbara Loe Fisher, the organization's president, in a prepared statement.

On Tuesday, Merck announced it was dropping its lobbying campaign to persuade states to make the cancer vaccine required for adolescent girls attending public school.