Should girls be vaccinated against human papillomaviruses that cause cervical cancer? That the question facing the use of Gardasil, a HPV vaccine.
Should girls be vaccinated against human papillomaviruses that cause cervical cancer? While most major health authorities in Canada, the US, and Europe support widespread vaccination with Gardasil, the first approved anticancer vaccine, others advocate a slower pace to assess the vaccine’s long-term effects.
The Gardasil vaccine protects against four types of sexually transmitted human papillomaviruses (HPVs) that contribute to genital warts and may cause negative changes in cervical cells. Types 16 and 18 are involved in about 70 percent of pre-cancerous lesions, abnormal growths, and cervical cancers. Types 6 and 11 cause about 90 percent of genital warts.
The vaccine has been approved for girls and women between nine and 26 years of age. Protection has been shown to last up to four years. The manufacturer, Merck, is running post-approval studies under a US Food and Drug Administration (FDA) directive to assess the need for boosters to maintain effectiveness beyond this period.
Limitations of Gardasil
Gardasil protects only against HPV types 16, 18, 6, and 11. The vaccine provides no protection against other HPV types that may cause 30 percent of cervical cancers and 10 percent of genital warts. Gardasil does not protect against sexually transmitted infections nor can it cure existing HPV infections, though there is some evidence it may mitigate additional growth and spread. All health authorities emphasize that sexually active women continue to need regular pelvic examinations and Pap smears even after vaccination.
Critics have challenged Merck’s efficacy and safety claims, contending that since the studies from which these claims are drawn were funded and conducted by the company, the results are biased.
But critics who challenge Merck for funding, designing, and conducting the studies that led to approval are essentially attacking the company for following procedures and regulations of the FDA, as well as comparable Canadian and European regulatory bodies. Not only did Gardasil undergo numerous robust clinical trials before approval in the US and Canada, but the work leading to the vaccine was conducted by researchers at Merck, the US National Institutes of Health (NIH), Georgetown University, the University of Rochester (New York), and Queensland University in Brisbane, Australia.
Trusting the Approval Process
The earliest laboratory studies that led to Gardasil began in 1991. In 2006 the vaccine received approval based on a total of 10 preclinical studies and 12 clinical studies. Its efficacy was assessed in four placebo-controlled, double-blind, randomized Phase II and III clinical studies. The four clinical studies, conducted internationally over two or more years, evaluated more than 20,000 women between 16 and 26 years of age, with follow-up periods ranging from between two to four years.
According to the NIH, the FDA, and Health Canada, the vaccine is highly effective in preventing persistent infections that cause precancerous cervical cell changes. Independent subsequent research has generally confirmed the company’s efficacy and safety claims.
Predicting the Future
Protecting children from cancer is laudable. Given the widespread and highly communicable nature of HPV, most girls who become sexually active will be exposed to HPV. But how likely is it that a girl will develop cervical cancer from HPV?
HPVs are involved in all cervical cancers, but few women with HPV infections develop the cancer. It is true that cervical cancer is a major killer worldwide; however, data from the developing world skew the mortality statistics significantly. In these areas the death rates from cervical cancer are inflated by the lack of screening and treatment.
In industrialized countries where good hygiene, safe-sex education, early screening, and good medical care are available, the incidence of cervical cancer is comparatively low and deaths even more rare. For example, 11,800 cases of cervical cancer (7.9 per 100,000) were reported in the US in 2004, but the mortality rate was only 2.6 per 100,000. Compare this to the 186,772 cases of breast cancer reported the same year, with a death rate of 27.5 per 100,000. Canada, Europe, and Japan have similar incidence rates.
Walking the Tightrope
In deciding whether or not to choose vaccination, parents may confront uncomfortable questions–when will our daughter become sexually active, how many partners will she have, what if one partner carries HPVs that expose her to a cancer that this vaccine may have prevented? In short, parents are being asked to balance the risk that their daughters will engage in future, possibly unsafe sexual behaviours against the risk of treating them with this new vaccine.
The younger the child, the more time parents have to evaluate the benefits and risks of HPV vaccination. Vaccination decisions may be easier if there is a family history of cervical or vulvar cancers. No question about it, though, the Gardasil breakthrough has made parenting a bit more complicated.