Herd protection seen with HPV immunization
Findings from a just-published study of young women ages 13-16 in Cincinnati are the first to document herd protection after introduction of the human papillomavirus (HPV) vaccine.1
The first HPV vaccine, the quadrivalent formulation Gardasil (Merck & Co.), was licensed for use in the United States in June 2006. The bivalent formulation Cervarix (GlaxoSmithKline Biologicals) was approved in 2009. HPV vaccines are routinely recommended for girls and boys ages 11 and 12. The vaccine series can be started beginning at age 9. Vaccination also is recommended for females ages 13 through 26 and males ages 13 through 21 who have not completed the vaccination series. Males ages 22 through 26 also may be vaccinated.2
Herd immunity, which is defined as a drop in infection rates among unimmunized individuals when a critical mass of individuals is immunized against a contagious disease, is an important public health goal, says Kevin Ault, MD, professor of gynecology and obstetrics at Emory University in Atlanta.
Much research has been published about the benefits to the individual who receives the HPV vaccination, says Ault. A body of evidence now demonstrates the vaccine's protection against genital warts and cervical cancer, anal cancer, vulvar cancer, and vaginal cancer, he notes. However, many of the public health policies that were made about who should get the vaccine were made on the assumption of herd immunity, Ault observes.
"Now that the vaccine has been out long enough, we are beginning to see some real-world research that confirms herd immunity," says Ault.
While the news about the vaccine's herd immunity effect is heartening, there are still so many people under age 27 who have not received the immunization, says Susan Wysocki, WHNP-BC, FAANP, president & chief executive officer of Washington, DC-based iWomansHealth, which focuses on information on women's health issues for clinicians and consumers.
HPV is ubiquitous, notes Wysocki. Clinicians should encourage parents and those under age 27 to obtain the vaccination. With more data developing about HPV and head and neck cancers, as well as other cancers, there are many more reasons to be vaccinated, Wysocki states.
"We have been looking for cures for cancer for as long as I can remember," she observes. "Isn't it better to prevent than cure?"
Review the research
To perform the current study, researchers at Cincinnati Children's Hospital Medical Center recruited 368 young women between the ages of 13 and 16 from two Cincinnati primary care clinics during 2006 and 2007. All young women enrolled in the study had sexual contact, but none were vaccinated. In 2009 and 2010, investigators recruited a different group of 409 young women in the same age range, more than half of whom had received at least one dose of the vaccine. Mean age was about 19 years for both groups of participants; most were African American and non-Hispanic.
To perform the analysis, researchers compared pre- and post-vaccination HPV prevalence rates. After propensity score weighting, the prevalence rate for vaccine-type HPV decreased substantially (31.7%-13.4%, P < .0001). The decrease in vaccine-type HPV not only occurred among vaccinated (31.8%-9.9%, P < .0001), but also among unvaccinated postsurveillance study participants (30.2%-15.4%, P < .0001).
The increase in nonvaccine-type HPV in vaccinated participants should be interpreted with caution, but warrants further study, study authors note. Larger studies with more representative samples are needed to definitively determine the public health impact of the HPV vaccine, said Jessica Kahn, MD, MPH, a physician in the division of Adolescent Medicine at Cincinnati Children's Hospital Medical Center, in a statement accompanying the study's publication. Kahn served as lead author of the study.
Providers need to advocate for early initiation of the HPV vaccine. Results of a new study indicate that waiting until the teen years might be too late. A separate research team at Cincinnati Children's Hospital Medical Center tested 259 females ages 13-21. Among the 190 who said they already were sexually active, 70% were already infected with HPV. Even among girls who'd had sexual experience without intercourse (sexual contact defined as genital, skin-to-skin contact), 11% were infected with HPV.3
In December 2011, the Advisory Committee on Immunization Practices of the Center for Disease Control and Prevention recommended the routine use of the quadrivalent HPV vaccine in boys beginning at the age of 11 or 12.4 Public health officials are looking for the routine use recommendation to aid in rapid uptake of the vaccine.
Australian public health officials are taking it one step further. Beginning in 2013, the quadrivalent HPV vaccine will be funded for all Australian 12- and 13-year-old boys as part of the country's National Immunization Program. Immunization of Australian females began in 2007, with a drop in cervical cancer documented in subsequent research.5 It is estimated that a quarter of new infections will be avoided by extending the vaccine to boys, Australian officials state.
References
- Kahn JA, Brown DR, Ding L, et al. Vaccine-type human papillomavirus and evidence of herd protection after vaccine introduction. Pediatrics 2012; 130(2):e249-256.
- Centers for Disease Control and Prevention. HPV vaccine information for clinicians. Fact sheet. Accessed at http://1.usa.gov/NiL7pk.
- Widdice LE, Brown DR, Bernstein DI, et al. Prevalence of human papillomavirus infection in young women receiving the first quadrivalent vaccine dose. Arch Pediatr Adolesc Med 2012; 166(8):774-776.
- Centers for Disease Control and Prevention (CDC). Recommendations on the use of quadrivalent human papillomavirus vaccine in males — Advisory Committee on Immunization Practices (ACIP), 2011. MMWR 2011; 60(50):1,705-1,708.
- Brotherton JM, Fridman M, May CL, et al. Early effect of the HPV vaccination programme on cervical abnormalities in Victoria, Australia: an ecological study. Lancet 2011; 377(9783):2,085-2,092.
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