While the HPV vaccine has been embraced by governments as an effective way to protect women and girls from cervical cancer, some have worried about its safety. Now, a new report confirms that reactions to the vaccine are rare.

The study found the vaccine has been generally safe since it was introduced, with reports of "adverse events" being fairly consistent with pre-licensing data. While more than 23 million doses of HPV vaccine have been given to women in the U.S., there have been only 12,424 reports of adverse reactions.

The one exception U.S. researchers have found is a slightly higher proportion of reports of fainting and blood clots.

The first HPV vaccine to be approved in Canada, called Gardasil, protects against four strains of sexually transmitted human papillomavirus that can cause genital warts and as many as 70 per cent of cervical cancers.

It is approved for females between the ages of 9 and 26 and many school boards across Canada have already begun programs to administer the three shots over six months needed to confer immunity.

Prior to the vaccine's approval, clinical trials were conducted on more than 21,000 women to look for side effects from the vaccine. Those studies found the rates of side effects were similar between women given the vaccine and those given a placebo shot.

But it is only when the vaccine is given to millions of women and girls that health authorities can detect side effects, both mild and severe, that are too rare to have been detected during those clinical trials.

For this study, published in JAMA, Dr. Barbara A. Slade, of the U.S. Centers for Disease Control and Prevention in Atlanta, analyzed reports of adverse events following HPV immunization from June 2006 through December 2008. They noted that for every 100,000 vaccine doses given, there were:

  • 8.2 reports of fainting
  • 7.5 local site reactions, such as swelling at the injection site
  • 6.8 reports of dizziness
  • 5.0 reports of nausea
  • 4.1 reports of headache
  • 3.1 reports of allergic reactions;
  • 2.6 reports of skin rash
  • 0.2 blood clots, autoimmune disorders, and Guillain-Barr� syndrome (a disorder that can cause temporary paralysis)
  • 0.1 for anaphylaxis and death.

 The report found nearly 1,900 episodes of fainting following vaccination, including 93 that had serious consequences, such as broken bones and head injuries.

"The post-licensure safety profile presented here is broadly consistent with safety data from pre-licensure trials," the authors conclude, noting that post-licensure monitoring is continuing.

But in an accompanying editorial, Dr. Charlotte Haug, of The Journal of the Norwegian Medical Association, in Oslo, finds the reports worrying, especially since she's not convinced that girls need the vaccine.

"Even if persistently infected with HPV, a woman most likely will not develop cancer if she is regularly screened. So rationally she should be willing to accept only a small risk of harmful effects from the vaccine," she writes.

Adolescent health specialist Dr. Miriam Kaufman disagrees. The physician at Toronto's Hospital for Sick Children says while side effects happen, there is a lot of good that comes from this vaccine. And she notes that while Pap screening can detect cervical cancer at its earliest stages, the rates of Pap screening in Canada are not as high as they should be.

"There are risks to immunizations. However, the protection is much greater than the risks involved. So without immunizations, more people would get cervical cancer and die from cervical cancer than from the vaccine," she told CTV Toronto.

It's estimated that about 1,350 women contract the sexually transmitted HPV each year in Canada, while about 400 women die of cervical cancer annually. It is the second most common type of cancer for women between 20 and 44.

Kaufman notes that incidents of fainting aren't generally a result of a fear of needles; more often, they occur about five to 10 minutes after a shot is given. She says why some patients faint isn't clear but it may be related to blood pressure. Fainting itself isn't dangerous, she notes; the danger comes from falling.

With a report from CTV Toronto's Monica Matys