In early 2007, as the pharmaceutical giant Merck began promoting its new vaccine Gardasil as protection against cervical cancer, Brooke Petkevicius was a nineteen-year-old freshman at UC Berkeley. She had seen the ads for the vaccine, and discussed getting it with her mother, whose gynecologist also had recommended it. On March 12, Brooke received the first of three doses. Two weeks later, she dressed to go running with a friend. As they reached the elevator, Brooke suddenly collapsed against the wall and had a seizure.

"She started shaking a lot," recalled the friend, Kristin Bietsch. "And her eyes went glazy a little bit." An ambulance rushed Petkevicius to the hospital, but doctors couldn't save her. Her autopsy indicated that she was killed by a pulmonary embolism, or blood clot, which had blocked the artery between her heart and lungs. "She had a whole bunch of little floating clots in her system," said her mother, Debra Sonner, recalling what doctors told her at the time.

Petkevicius had been healthy and happy, by all accounts. She didn't smoke or use drugs, and was training to run a half marathon. The only unusual thing that Sonner noticed about her daughter's health was that she had just taken Gardasil. When she went to clean out her daughter's dorm room, she encountered the completed insurance paperwork that Brooke was preparing to mail. "Of course, I found it and realized that she had just had the shot." Sonner immediately wondered whether her daughter's death was "some kind of reaction."

Her suspicions prompted health workers to report Brooke's death as one of what are now 4,500 Gardasil-related reports in the federal government's Vaccine Adverse Event Reporting System. About 75 percent of these reports were for minor expected side effects — pain at the injection point, fainting, and nausea, for instance.

But according to researcher Dee Grothe of the Washington foundation Judicial Watch, who read nearly 4,000 of the reports, the remaining 25 percent involved more serious issues, including paralysis, convulsions, and circulatory problems. Grother says the surveillance database now contains eleven Gardasil-related death reports, including the story of a woman who died of a blood clot three hours after getting the vaccine and a healthy twelve-year-old who died in her sleep three weeks later.

Based on the first death reports, including that of Brooke Petkevicius, the federal Centers for Disease Control pointed the finger at birth-control pills, not Gardasil. "Preliminary data indicate that the two women who died of blood clots were taking birth-control pills, and blood clots are a known risk associated with birth-control pills. All four deaths are being fully investigated but none appear to be caused by vaccination," according to the CDC on June 28, 2007. With regard to Gardasil, the CDC wrote, "Since more than 5 million doses have been distributed, some deaths will occur coincidentally following vaccination (but not due to vaccination)."

Gardasil researchers at the Medical College of Georgia and at Dartmouth University believe the vaccine is quite safe and are firmly convinced there's no scientific basis to blame Gardasil for the serious adverse reactions. Merck officials declined a request to comment for this story.

Still, debate is growing. All these reports from health-care workers and individuals have some people worried about the drug's side effects and safety. Meanwhile, the National Vaccine Information Center, a consumer organization concerned with vaccine safety, has raised concerns about women who have taken Gardasil being subsequently struck by Guillain-Barré Syndrome, a potentially fatal illness. Judicial Watch and the center have publicly questioned whether Gardasil was adequately tested for cross-reactions with other drugs and vaccines.

For her part, Grothe is not convinced that the blood clots and circulatory problems being reported by some Gardasil users are random events unrelated to the vaccine. "Some are pretty hard to discount as being a reaction," Grothe said. "When a patient dies of a blood clot three hours after getting a Gardasil vaccination, that's pretty consistent to me."

I am a 5-4, 120-pound, 17-year-old girl. I am healthy and have never had problems with shots, allergies or fainting. Yesterday (Jan. 3, 2008), I went to the doctor for a routine checkup and was advised by my doctor to receive several shots, including the first Gardasil vaccine.

"About 20 seconds after I received the shots, I felt nauseous and dizzy. I fainted and began to display seizure-like symptoms: My eyes rolled back in my head and I started shaking. After that, I was unconscious for 3-5 minutes. I had a severe headache the entire day and soreness where I received the HPV shot, which I thought was perfectly normal.

"The nurse also reassured me that fainting was normal, and that it was due to me having four shots given in a row; she said it had absolutely nothing to do with the vaccines. Before agreeing to the shots, I asked my doctor what the side effects would be. She told me that there were no serious side effects (just soreness and possibly mild fever) and that it was medically fine for me to have four shots given at once...

"I am sick over the idea that young girls are being recommended this potentially harmful shot, and that very few people seem to be doing anything about it."

— R.B., Madison, Wisconsin, Gardasil user

Gardasil has been shown in clinical studies to be virtually 100 percent effective at preventing the infection of four strains of human papillomavirus (HPV), the sexually transmitted virus that causes genital warts. Two of those strains are believed to be responsible for causing about 70 percent of cervical cancer. The vaccine also has been shown to be about 40 percent effective at stopping another type of HPV that is the fourth-most-common strain linked to cervical cancer. And there is some evidence that it also offers some protection against vaginal and vulvar cancer.

Nearly everyone gets some form of HPV infection, but most fight off the infection with a natural immune response. However, in some women, the infection develops into an identifiable precancerous condition of the cervix. A woman's chance of getting cervical cancer in her lifetime is about 1 in 142, according to the National Cancer Institute.

For decades, the primary defense against cervical cancer has been the Pap smear. Regular Pap tests allow physicians to identify the precursors to cervical cancer at its early stages, when it's nearly 100 percent treatable. It can take up to ten years for an HPV infection to turn into cervical cancer. In the United States, about 10,000 women will get cervical cancer every year and nearly 4,000 will die from it.

Pap smears have helped reduce the rate of cervical cancer in the United States by 70 percent in the last half-century. The greatest risk for cervical cancer lies with those 11 percent of women who don't see their health-care provider for Pap smears, or who can't afford treatment. That means that the poor and uninsured are at the greatest risk.

That's why most of the world's 250,000 deaths from cervical cancer are in developing countries, where regular health-care screenings are unavailable to most women. The majority of the gains against cervical cancer expected from Gardasil and future HPV vaccines will be in those developing areas of the world, where it will be more cost-effective to treat women with vaccines than to set up ongoing health clinics to examine them on a regular basis.