TUESDAY, Aug. 18, 2009 (HealthDay News) -- The vaccine that protects against human papillomavirus (HPV), a cause of cervical cancer, appears safe, with relatively few serious side effects, according to a new U.S. government study.
The study, which included data from the voluntary Vaccine Adverse Event Reporting System (VAERS), found that the rate of serious adverse events for the vaccine, marketed under the brand name of Gardasil, was similar to data from earlier clinical trials, except for rates of fainting and blood clots.
For every 100,000 doses of HPV vaccine distributed, the study found 8.2 episodes of fainting and 0.2 episodes involving blood clotting. The study is published in the Aug. 19 issue of the Journal of the American Medical Association.
"Basically, we didn't see anything that surprising. This is a safe vaccine," said the study's lead author, Dr. Barbara Slade, a medical officer in the immunization safety office at the U.S. Centers for Disease Control and Prevention. "Syncope [fainting] is the most commonly seen adverse event."
As for the increased rate of serious incidents of blood clotting, Slade said that most of the girls or women who had such problems had other characteristics that increased their risk for clots.
"It's a complicated issue," she said. "Most of these girls had another risk factor for blood clots, but we don't want to dismiss the blood clots. We need to know if it's something that's truly unrelated, and we're recommending that this finding be looked at a little bit closer."
In June 2006, Gardasil was licensed for use in girls older than 9 years to prevent infection from four types of HPV. HPV is a virus known to cause genital warts and cervical cancer. Two types of HPV covered by the vaccine, HPV-16 and HPV-18, cause about 70 percent of cervical cancers worldwide. The vaccine is given in three doses.
In clinical trials conducted before licensing, researchers found that the rates of adverse events were similar in girls and young women who received the vaccine compared with those who received a placebo injection.
For the new study, researchers from the CDC and the U.S. Food and Drug Administration reviewed data from VAERS, the voluntary system that enables anyone to report a vaccine-related side effect. Slightly more than two-thirds of the information on Gardasil was provided to VAERS by the drug's manufacturer, Merck & Co.
The researchers reviewed data from the time Gardasil was approved in 2006 through December 2008. During that time, 23 million doses of Gardasil were distributed throughout the United States, Merck said.
More than 12,000 reports of adverse events after vaccination were reported to VAERS. Of those, 772 were described as serious, including 32 deaths, the study found.
Slade said that when the researchers reviewed the deaths, they couldn't discern any pattern. Those who died were of different ages, there wasn't a common cause of death, and there wasn't a consistent time after vaccination that these deaths occurred.
"While this is heart-rending for the family involved because you don't expect deaths in this age group, our general feeling is that they're not vaccine-related," she said.
Other reported adverse events included local reactions, such as redness, swelling or pain at the injection site, dizziness, nausea, headache, allergic reactions and autoimmune disorders.
"We're pleased with the JAMA paper as it confirms the safety profile of Gardasil," said Dr. Richard Haupt, executive director of clinical research at Merck Research Laboratories. "The benefit-to-risk profile is very favorable," he added.
Dr. Len Lichtenfeld, deputy chief medical officer for the American Cancer Society, said it won't be making any changes to its recommendations, which suggest that young women receive the Gardasil vaccine to protect against some cervical cancers. But, he added, this study "is not the final or definitive answer."
Lichtenfeld pointed out, as did the study authors, that because VAERS is a voluntary system, it might underestimate the actual number of adverse events because some could go unreported. "More specific scientific studies need to be done," he said.
As for the episodes of fainting, Merck -- as well as the CDC -- recommends that anyone receiving the vaccine stay in the doctor's office for at least 15 minutes after receiving a shot.
The CDC's Slade also recommended that parents drive their teens to their appointments so the teens are not driving if a fainting episode should occur. And, because vaccines are often administered during physicals for which people have been asked to fast, Slade also suggested eating a quick snack and drinking something before getting the vaccine but after having blood drawn for the physical.
The U.S. Centers for Disease Control and Prevention has more about the HPV vaccine.