High Stakes
The sexually transmitted human papillomavirus (HPV) is the leading cause of cervical cancer, as well as a source of some head and neck cancers. In 2006, an approved three-series vaccine was recommended for adolescent girls, and a recent study led by Amanda Dempsey, M.D., assistant professor of pediatrics and communicable diseases, assessed vaccination rates at U-M clinics in southeastern Michigan. Dempsey serves as a consultant to Merck on male HPV vaccination.
Q: Your study found HPV vaccination rates to be low among adolescent girls — about 15 percent — as did a national study in 2007. Why is the rate so low when the stakes are so high?
A: It’s important to remember that with any new vaccine there’s a curve of usage, so it’s not completely unexpected that vaccine uptake isn’t optimal in the first year or two. But the HPV vaccine has a few aspects that are making people a bit more reluctant to try it than other vaccines in the past. The fact that it’s a vaccine against an STD causes some parents concern that they may be sending mixed messages to their children about their beliefs on sexuality and morality. Some parents are concerned because it’s a new vaccine; we saw similar issues with the H1N1 vaccine this past flu season. And In general, the public has over the last couple decades developed vaccine fatigue. As more and more vaccines are introduced, the public is seeing fewer diseases because vaccines are so successful, so there’s a lack of connection with the continuing importance of high vaccination rates.
We’ve actually done another study that asked mothers why they did or didn’t consent to have their daughters vaccinated against HPV. The main reasons were reluctance because of safety concerns; believing the vaccine wasn’t necessary for whatever reason — their daughter is too young, they didn’t believe it was important to give so soon before their daughter might be sexually active; or there’s some moral issue — some people might say their daughter isn’t going to have sex till she’s married so she’s not at risk at all, which is actually a common misconception. Even if that’s the case, if the husband has had sex previously, the risk could be present, as it could be in nonconsensual sex.
Q: What can be done to increase HPV vaccination rates?
A: There’s going to be a need for multiple types of intervention to address the various reasons people don’t initiate vaccination of their daughters. Some of the easier ones to fix are things like lack of access to care — people who have a difficult time getting to a doctor’s office because of transportation issues or clinics not being open at times when they’re not at work. These are some of the easier infrastructure problems we can work on. The bigger problems are people’s beliefs and attitudes about the vaccine, so education will be important — it’s hard to change people’s opinions.
Q: What effect could high vaccination rates have on cervical cancer?
A: Time is the only way we’ll know for sure, but there have been a lot of mathematical modeling studies that have tried to address that specific question. When they assume very high levels of vaccine uptake among adolescents, somewhere between 70 and 100 percent, the models predict that cervical cancer rates would decrease dramatically — by about 70 percent, because we believe that about 70 percent of cervical cancers are caused by the types of HPV the vaccine protects against.
What’s also important to note is that there are far many more women who are suffering from pre-cancerous lesions, so the cancer cases actually represent only the tip of the iceberg. The actual number of women who are being followed, treated and tested for all these other precancerous lesions is huge. In the U.S., at least, where cancer screening programs are fairly effective, we’re going to see an even bigger impact on the need for follow-up and treatment of these precancerous conditions related to the HPV types the vaccine protects against.
Q: How many types of HPV are there, and how many does the vaccine protect against?
A: There are more than 100 types of HPV. Approximately 25 types are associated with cervical cancer; this vaccine protects against two of the cervical cancer-causing types. There’s some evidence of partial cross-reactivity with one or two other types, so at most we’re talking about four cancer-associated HPV types. Manufacturers are working on a vaccine against nine types, and future iterations might protect against even more. They are working toward eliminating the HPVs that are most associated with cervical cancer. It’s not a panacea, but getting the vaccine is certainly a good way to dramatically reduce your risk of developing cervical and other cancers.
Q: What is the efficacy of the HPV vaccine?
A: That’s a big question, and one we can’t answer until enough time has gone by, but at this point the vaccine has maintained very high efficacy over a period of six-and-one-half years.
Q: How prevalent is HPV?
A: Estimates are that at least 80 percent of sexually active adults will have acquired at least one HPV infection by age 50. The vast majority of infections don’t cause any clinical symptoms; they resolve on their own. It’s really hard to predict of those who do have an infection, which ones will go on to develop severe sequelae as a result of that infection.
Q: Universal vaccination is recommended for girls ages 11-12, yet you found that vaccination rates in this age group are significantly less than girls age 13 and older. Why is that?
A: Parents have concerns about the duration of immunity and the possible need for repeated vaccination in the future. They see age 11 as too early. We target 11- to 12-year-olds because we want to reach the population before virtually any of them are sexually active. I think parents underestimate the risk because they don’t see their 11- to 12-year-old as an adolescent yet, so sex isn’t really on the radar. It’s important to realize that there’s a fair proportion of 13- to 15-year-olds who become sexually active — it’s hard to determine in each individual family when that’s going to happen. There’s some evidence that HPV can be transmitted by means other than just penetrative intercourse — for example, digital or oral transmission. I don’t think a lot of parents are aware of that.
I think that’s another reason uptake has been slow — there’s a lack of immediacy about the vaccine, like waiting a couple years is no big deal. As a generalization, it’s hard to predict for whom that would be a reasonable strategy and for whom it would not. Focusing on getting everybody before they’re sexually active is the most conservative strategy. Since the vaccine efficacy data has gone on longer, we have more of a sense that vaccinating at 11 will still be effective in the higher risk years.
It’s much like the hepatitis B vaccine that initially started as an adolescent vaccine for the sexual transmission of that virus. That didn’t work very well, and eventually the vaccination got moved to infancy and now all infants get vaccinated against hepatitis B and they’ve shown the duration of immunity lasts long enough that there’s no need for boosters in the future. It’s possible that the HPV vaccine might follow a similar trajectory over the next couple decades.
Q: Your study found that two of the groups at highest risk for cervical cancer — minorities and those with public insurance — were found to be less likely to complete the vaccination series. Were they also less likely to initiate the series?
A: If you are an underrepresented minority in our study, or have public insurance, you are more likely to start the vaccination series — get the first dose — but less likely than those with private insurance or non-minorities to complete the three-dose series. It’s important to remember that vaccination series completion is really the only way as far as we know to get adequate protection against HPV. Getting one dose is better than getting none, but is not, we think, protective in preventing HPV. So the fact that minorities or those who are lower-income have a lower rate of vaccine series completion is very concerning because those are the groups at highest risk and who are less likely to participate in routine cervical cancer screening programs in the future. One of the really important areas to focus on is getting these high-risk populations completely vaccinated with the three-dose series.
Q: What is the status of HPV vaccination for males?
A: The national Advisory Committee on Immunization Practices has issued a permissive recommendation, which means that any male between the ages of 9 and 26 who wants the vaccine should be able to receive it. The FDA voted to include the HPV vaccine in the Vaccines for Children Program, which is a public vaccine purchasing program that provides free vaccine to uninsured or underinsured children age 18 and under. It was an important step because even though the vaccine is not specifically recommended for males as it is for females, the addition of the vaccine to the vaccine formulary really opened the door for a lot of people who might want the vaccine to receive it.
Q: Now that links between HPV and head and neck cancer have been established in both men and women, will that help the vaccine to catch on?
A: That, combined with males being eligible for the vaccine. As more and more data show the impact that HPV infection has on a variety of cancers — not just among women, not just cervical cancer — it provides more compelling evidence that the vaccine is important. My hope is that in the future we can say this is a vaccine against a variety of cancers and it’s important for everyone to get.
Interview by Rick Krupinski