Wednesday, March 11, 2009
There is not enough evidence to confidently state that two popular vaccines against the human papillomavirus (HPV) will reliably prevent against the development of cervical cancer, according to two articles published in the New England Journal of Medicine.
“Despite great expectations and promising results of clinical trials, we still lack sufficient evidence of an effective vaccine against cervical cancer,” wrote Charlotte J. Haug, editor of The Journal of the Norwegian Medical Association, in the first article. “With so many essential questions still unanswered, there is good reason to be cautious.”
Haug noted that Merck’s Gardasil and GlaxoSmithKlein’s Cervarix have only been studied clinically for six and a half years at the most, and have only been on the market since 2006. This means that researchers still do not know if the vaccines are effective against HPV over the long term, or what cancer-related side effects they might have. For example, protecting the body from infection with certain HPV strains might have unforeseen immunological side effects, reducing the body’s resistance to other varieties.
Due to the newness of both vaccines, it is also not yet been possible to see whether they actually reduce cervical cancer rates. Normally, it takes years of HPV infection before cancer can develop – more time than either drug has been studied.
In the second article, a pair of Harvard researchers noted that HPV vaccination is not necessarily a cost-effective way to protect against cervical cancer. Current screening methods such as Pap smears have been very effective in reducing the death rate of cervical cancer already, but such tests must continue even after receiving an HPV vaccine. Even at their best, the vaccines do not protect against all cervical cancer strains that can cause cancer; a woman who has already been exposed to one of the strains in the vaccine will get no benefit from it.
“I believe the vaccine is a great advance,” said Philip Davies of the European Cervical Cancer Association, “but we have to implement it properly to get the benefits, and that hasn’t happened.”