Weighing benefits and risks of HPV vaccine

(Ivanhoe Newswire) -- A new study reports quadrivalent human papillomavirus recombinant vaccine (qHPV), used since 2006 to prevent genital infection in women, is associated with a higher than expected proportion of fainting and blood clots.

In June 2006 the Food and Drug Administration (FDA) licensed the qHPV vaccine for females age 9 to 26 years to prevent infection with genital HPV types 6, 11, 16, and 18. Shortly thereafter, the Advisory Committee on Immunization Practices recommended routine vaccination of females age 11 to 26 years with qHPV.

"The viruses HPV-16 and HPV-18 can cause cervical cancer, other anogenital cancers, and precancerous [lesions] . . . and are responsible for about 70 percent of cervical cancers worldwide," the authors wrote. "The viruses HPV-6 and HPV-11 are the most common causes of genital warts." Barbara A. Slade, M.D., M.S., of the Centers for Disease Control and Prevention, Atlanta, and colleagues analyzed reports of adverse events following qHPV immunization from June 1, 2006, through December 31, 2008.

"With more than 23 million qHPV doses distributed in the United States as of December 31, 2008, post-licensure safety monitoring can detect [adverse evens] too rare to have been detected during pre-licensure trials," the researchers noted. The pre-licensure clinical trials involved more than 21,000 women. Adverse incident reports following immunization were similar in the vaccine group (59 percent) and the placebo group (60 percent).

Of 12,424 adverse reports in the new study, 772 were serious, including 32 reports of death. Analyses indicated a disproportionally high incidence of fainting and blood clots.

"The post-licensure safety profile presented here is broadly consistent with safety data from pre-licensure trials," the authors concluded. "Post-licensure monitoring will continue, and identified signals may be evaluated using epidemiologic observational studies."

In an accompanying editorial, Charlotte Haug, M.D., Ph.D., M.Sc., of The Journal of the Norwegian Medical Association, Oslo, Norway, commented, "Whether a risk is worth taking depends not only on the absolute risk, but on the relationship between the potential risk and the potential benefit. If the potential benefits are substantial, most individuals would be willing to accept the risks. But the net benefit of the HPV vaccine to a woman is uncertain. 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."

SOURCE: Journal of the American Medical Association ( JAMA), August 19, 2009