By Jeanne Lenzer, Medical Investigative Journalist
Merck’s promotion of Gardasil, its vaccine against the human papilloma virus (HPV), has a complicated history. First there was the exuberant claim about its reputedly great effectiveness in preventing cervical cancer. Now comes the recommendation last month from the Centers for Disease Control and Prevention, that all 11- and 12-year-old boys should be given the vaccine.
Of Science and Truthiness
The vaccine for boys is important, say advocates, because reducing HPV in boys will reduce transmission to girls and women—only 32 percent of whom have been getting the shots to date. Giving the shots to boys, they say, promotes gender equity. As a bonus, the vaccine may protect against oral and anal cancers in men who have sex with men.
Since a key part of the rationale for vaccinating boys is to protect girls, it’s worth a moment to examine the claims about reducing cervical cancer deaths. Merck won approval for Gardasil from the Food and Drug Administration in June 2006. On May 10, 2007, Merck published the results of a study in the New England Journal of Medicine that claimed an astounding 98 percent efficacy in preventing changes in the cervix used as a marker for cervical cancer.
But that statistic begs closer examination.
To achieve the 98 percent efficacy claim, Merck excluded from analysis anyone who “violated” the study protocol. In other words, all real-world problems that arose were excluded from analysis. Problems like girls who refused to take a second or third shot after they became sick and (correctly or incorrectly) blamed the vaccine. Or doctors who incorrectly gave the vaccine to someone who shouldn’t have received it. While it’s worth knowing how effective the vaccine is when it’s used exactly as it should be, for a public-health decision, it’s not as relevant as its real-world effectiveness.
To Merck’s credit, they reported that when all women in the study were analyzed, the vaccine’s efficacy dropped to 44 percent. Still, 44 percent might be considered a smashing success when you’re talking about saving lives. Except for one thing: the numbers get worse. The 44 percent benefit included only those women with the two specific cancer-causing HPV strains found in the vaccine. But when the researchers looked at negative cervical changes from any causes, they found that changes occurred in unvaccinated women at a rate of 1.5 events per 100 person-years, while vaccinated women had 1.3 events—dropping the benefit to 17 percent.