The HPV Vaccine Could Do Even More
- Alexis Bigham
- Monday, February 17th, 2014
By Debbie Saslow, PhD
The HPV vaccines (Gardasil and Cervarix) have been recommended for girls in the US for nearly 10 years. They protect against human papillomavirus (HPV), the virus that causes most cases of cervical cancer, and Gardasil also protects against nearly all cases of genital warts. Uptake of HPV vaccination has been slow in this country, though; less than 35% of girls have gotten all 3 recommended doses.
Despite low vaccination rates, we have already seen HPV infections (related to the types of HPV targeted by the vaccines) drop by 56% in the United States. In countries that have higher vaccine rates, there are even larger drops. Indeed, data published last year suggest that higher vaccination rates could reap great benefits.
The potential to eliminate genital warts
A study from Australia, where more than 70% of adolescent girls are vaccinated, suggests that in countries where vaccine coverage is high, genital warts may be eliminated in the coming decades.
The government-funded Australian HPV vaccine program has provided free vaccine in schools to 12- and 13-year-old girls since 2007. From 2007-2010, free vaccine was also offered to girls and women ages 14-26.
The number of cases of genital warts among young people has dropped dramatically since the program began.
Before the introduction of HPV vaccination, 9.6% of young women seen in sexual health clinics were diagnosed with genital warts; 5 years later only 2.7% of female patients received this diagnosis. For women under age 21, that rate dropped to less than 1%! All cases of genital warts in this younger age group occurred in women who had not been vaccinated.
Boys were not included in the program until 2013, and few males in Australia were vaccinated. Even so, the number of young male patients diagnosed with genital warts fell dramatically, too. This is most likely explained by indirect protection by those who have been vaccinated. In contrast, no changes in rates of genital warts were observed in women or men over age 30, who are not eligible for the vaccine.
Fewer cervical pre-cancers
Of course, protecting girls from cervical cancer is the primary goal of the HPV vaccine. The time from HPV infection to cancer can be decades, so it will take more time to see the impact of vaccination on cancer rates. The fact that there are fewer cases of genital warts in those who got the vaccine is an earlier marker of vaccine success.
Based on the trends seen in Australia, it is expected that similar dramatic decreases in cervical (and other) cancers will be observed in coming years. Indeed the number of high-grade abnormal Pap test results ("pre-cancers") has already declined in Australian young women. The decreases are expected to happen more slowly in countries with lower uptake of HPV vaccines, such as the U.S.
The potential to reduce oral cancers
HPV is also linked to other types of cancer besides cervical, notably cancers of the throat and tonsils, and it is hoped that HPV vaccination will protect against oral cancers. A study from Costa Rica suggests it can.
In this large vaccine study, researchers tested for the presence of oral HPV 4 years after vaccination. Because we do not have a way to detect oral pre-cancers, it is not possible to predict whether the vaccines will be effective. Nevertheless, this study found only 1 oral HPV infection among girls who had been vaccinated, compared to 15 infections in girls who had not been vaccinated.
The study, while preliminary, provides promising evidence that HPV vaccines might prevent oral HPV infections, and may also have a significant impact on how many throat and tonsil cancers occur.
The challenges of getting recommended HPV vaccines
With evidence mounting that the HPV vaccine provides a lot of protection, why aren't more US girls getting it?
A survey of parents who chose not to vaccinate their daughters against HPV showed the five most common reasons are that parents:
1. Did not think the vaccine was needed or necessary
2. Said their child was not sexually active
3. Had concerns about vaccine safety or side effects
4. Lacked knowledge about the vaccine or HPV
5. Did not receive a recommendation from the child's health care professional
Eighty-four percent of girls who have not been vaccinated against HPV had a health care visit at which time they received another vaccine. These are major missed opportunities. If all girls ages 11 years and older who had a health care visit and received another vaccine had also received HPV vaccine, HPV vaccination rates could have reached over 92%.
Education of parents about the vaccine, why it's needed, the importance of vaccinating prior to the onset of sexual activity, and its excellent safety record will help increase vaccine uptake in this country. Education of providers about the importance of recommending the vaccine will also increase the number of girls being vaccinated.