The HPV (human papillomavirus) vaccine is an important weapon in the battle against cervical cancer: Girls and young women who receive it dramatically lower their risk of HPV infections and thus of getting the cancers they can cause. But so far the vaccine has been deemed effective only when all three of its recommended doses are delivered.

Doses of the HPV vaccine Gardasil are shown at a pharmacy in Cambridge, Mass. (J. B. Reed/Bloomberg)

Reporting in the American Cancer Society journal Cancer, Abbey Berenson and Jacqueline Hirth of the University of Texas Medical Branch and their co-authors analyzed data for nearly 272,000 privately insured females who had initiated the vaccine series. They found that while the number of girls who got the first shot rose during that time, the percentages of girls who got all three injections dropped from around 50 percent in 2006 to just over 20 percent in 2009. ( Those numbers varied a bit across age groups.)

The study further found that those who were 13 and older were less likely than those ages 9 to 12 to get all three shots and that those who completed the series were more likely to have received the shots from obstetricians/gynecologists than from pediatricians. Overall, just over 38 percent of those who initiated the series got all three shots within a year.

The authors suggest that physicians may not be doing a very good job of reminding patients (and their parents) that all three shots are required. And the marketing campaign that helped launch the HPV vaccine Gardasil in 2006 "never addressed the three shots," Berenson says. (The current Gardasil Web site does mention, though not particularly prominently, that the vaccine is delivered via three shots.)

Girls and young women are to receive a second dose of HPV vaccine one to two months after the first shot and a third six months after the first shot. The vaccination has developed a reputation as being extremely painful (my own daughter will vouch for that). But this study was designed to determine whether girls and young women stop short of getting all three injections, not why they might do so.

Berenson says, "Our goal is that this important message reaches the general public. We want to reach that parent who will say, 'Oh, my God! My daughter had only one injection. I didn't know she needed a second and a third.'"