By Sydney Philpott
Human papillomavirus (HPV) is a very common sexually transmitted infection. According to the World Health Organization (WHO), most sexually active women and men will have an HPV infection at some point in their lives. While HPV infections usually go away on their own, certain types persist and then serve as the primary cause of cervical cancer. Globally, HPV leads to about 600,000 new cases of cervical and genitourinary cancer each year, with about 26,900 cases in the United States alone.
In 2006, HPV vaccination became available worldwide and was recommended by the WHO and the Centers for Disease Control and Prevention (CDC) for girls age 9-26 and recommended for boys of the same age group in 2011. After just 5-6 years, studies in the United States found that HPV infections in girls age 14-19 dropped 64 percent, risk of cervical pre-cancer was lowered by 47 percent, and there was a 61 percent reduction in treatment for genital warts (infographic). The WHO estimates that two-thirds of new cases of cervical cancer could be prevented if 80 percent of those age-eligible were vaccinated worldwide.
Despite these improvements, vaccination rates in the United States have remained low. On average, only 60 percent of girls age 13-17 initiate the HPV vaccination series and 39.7 percent receive all three recommended doses, while only 41.7 percent of boys initiate and 21.6 percent complete the series. Additionally, there are clear racial and socioeconomic disparities for vaccination in the United States – but these often move in a direction opposite from many health behaviors. Among adolescent girls age 13-17 in 2014, 66 percent of blacks and Hispanics had at least one dose of the HPV vaccine, while 56 percent of whites did. Similarly, 67 percent of those below the poverty line started the series, while only 58 percent above did.
These numbers, though, change a bit when looking at the percentage of girls completing the full three-dose series once they start it, suggesting that efforts that drive initiation of the vaccine fall off in certain groups when it comes to completing the entire series. Of girls who started the series, 68 percent of those living below the poverty level and 69 percent of those living above went on to complete the 3 doses – nearly identical numbers. Similarly, over 70 percent of Hispanics and whites completed the series once they started, whereas only 62 percent of blacks did.
While the relatively high vaccination initiation rate in African Americans is heartening, it's also important to ensure that as many girls as possible get subsequent doses so they are as protected as possible in the future. Currently, African American women are more likely to be diagnosed with cervical cancer at later disease stages and die at almost twice the rate compared with non-Hispanic white women. Improving rates of HPV vaccination and completion across all groups can help narrow such cancer disparities.
Furthermore, recent systematic reviews examining efforts to increase HPV vaccination use in the U.S. have conflicting conclusions, and the relative success of these interventions fell short of national averages and stated vaccination goals.
Compared to the United States, other countries have had considerably more success achieving high HPV vaccination rates. Through implementation of school-based vaccination programs, Scotland reported 81 percent three-dose vaccination in 2011, England reported 76 percent in 2010 and Australia 73 percent in 2014. In 2013, the United States reported that only 37.6 percent of adolescent girls age 13-17 had all three vaccine doses.
These discrepancies may be due to the three-dose requirement remaining a substantial barrier to successful HPV vaccination in the United States. However, recent evidence indicates that fewer than three doses may be protective. Brotherton et al. found that less than three doses provides some protection against cervical disease in Australian women, even when measured within 5 years in a population including those who were sexually active at the time of vaccination. Therefore, adolescents in the United States, and other regions with low vaccination rates, may benefit from even partial vaccination. Updated recommendations for less than three doses could also lead to reduced costs for developing countries as well as broader uptake and access to vaccination. In the United States, nearly half of girls age 13-17 have received two doses of the HPV vaccine.
The ability to also test women for HPV is changing the approach to screening for cervical cancer, especially as more and more women are being vaccinated against HPV.
Since HPV is the direct cause of nearly all cervical cancers, women who are found to have HPV can be followed more closely to see if they clear the infection, or if they have or develop cancer or pre-cancer.
In the United States, the HPV test is most often recommended along with a standard Pap test in women 30 and older. This is called co-testing. In 2014, however, the FDA approved the stand-alone HPV test as a method of cervical cancer screening, and certain professional organizations now strongly suggest that the HPV test can be used on its own as an effective alternative to standard Pap tests in most women being screened for cervical cancer.
In Australia, the National Cervical Screening Program will implement a switch in 2017 from Pap testing every two years for those age 18-69, to HPV screening alone every five years for those between the ages of 25-74. This screening transition is expected to continue to reduce cervical cancer mortality while vastly reducing the burden on women.
Fewer numbers of doctor visits and stressful, time-consuming follow-ups for positive screening tests will be a major saving for women. Improving our ways of summarizing such benefits of HPV vaccination across life from 18 to 69 could help frame vaccination as a benefit to women far beyond just reducing cervical cancer incidence.