HPV vaccine’s effectiveness queried

New data on the controversial HPV vaccine designed to prevent cervical cancer have raised serious questions about its efficacy, researchers are to report today, undercutting efforts in many states to make vaccination mandatory.

Although the Merck vaccine, called Gardasil, blocked nearly 100 percent of infections by the two HPV strains it targets, it reduced the incidence of cancer precursors by only 17 percent overall.

Part of the reason was that many of the teenage girls and young women in the three-year study had already been exposed to the virus, according to the report in the New England Journal of Medicine.

But the data also hinted that blocking the targeted strains may have opened an ecological niche that allows the flourishing of HPV strains previously considered to be minor players, partially offsetting the vaccine’s protection.

In an accompanying editorial, Dr. George F. Sawaya and Dr. Karen Smith-Carter of the University of California, San Francisco, called the benefits of the vaccine “modest” and said young women and their parents should take “a cautious approach” to vaccination.

“The effect is fairly small,” Sawaya said in a telephone interview. “The recommendation for widespread vaccination of women after they become sexually active may need to be re-thought.”

The maker of the vaccine, Merck & Co., said the studies clearly showed that the vaccine prevents infections from the two HPV strains and reduces the number of precancerous lesions caused by them.

Immunologist W. Martin Kast of the University of Southern California’s Keck School of Medicine, who was not involved in the research, said he believed the study had not gone on long enough.

“In a three-year follow-up, it is very hard to reach statistical significance in a disease process that takes about a decade to fully develop,” he said. “Thus, it is not fair to state that the vaccine is not effective.”

Gardasil was approved by the Food and Drug Administration in June.

The Centers for Disease Control quickly recommended that all women ages 11 to 26 receive the vaccine. The American Cancer Society seconded that recommendation, although they concluded that there was “insufficient evidence” of benefit among women ages 19 to 26 because so many had already been exposed to the virus.

At least 24 state legislatures have introduced bills calling for mandatory vaccination of girls in their early teens or younger.