For women with human papillomavirus (HPV) infection, use of the HPV-16/18 vaccine will not accelerate reduction of the virus and should not be used to treat the infection, according to a study in the August 15 issue of JAMA.
HPV vaccines were designed to prevent HPV infection and the development of cervical precancers and cancer. Some research has suggested that HPV vaccines could help clear the virus in women already infected, according to background information in the article.
Allan Hildesheim, PhD, of the National Cancer Institute, Bethesda, Md., and colleagues conducted a study to address the question of whether women positive for HPV DNA should be encouraged to receive HPV-16/18 vaccination to induce or accelerate clearance of their infections. The trial was conducted in two provinces of Costa Rica and included 2,189 women age 18 to 25 years who were positive for HPV DNA. Participants were randomly assigned to receive three doses of HPV-16/18 vaccine (n = 1,088) or a control hepatitis A vaccine (n = 1,101) over six months.
There was no evidence that HPV vaccination significantly altered rates of viral clearance. At the 6-month visit, rates of clearance were 33.4 percent vs. 31.6 percent for HPV-16/18 among participants who received the HPV vaccine and the control vaccine, respectively. At the 12-month visit, rates of clearance among participants in the HPV group and the control group, respectively, were 48.8 percent vs. 49.8 percent for HPV-16/18.
There was no evidence of vaccine effects with further analysis on selected study entry characteristics reflective of disease extent, including HPV-16/18 antibody results, cytologic results, and HPV viral load. Similarly, no evidence of vaccine effects was observed in analyses stratified by other study entry parameters thought to potentially influence clearance rates and efficacy of the vaccine, including time since sexual initiation, oral contraceptive use, cigarette smoking, and concomitant infection with Chlamydia trachomatis or Neisseria gonorrhoeae.
These findings have important clinical implications. For example, in countries where HPV DNA testing is incorporated in cervical cancer screening and prevention efforts, adult women who have abnormal Papanicolaou test results induced by HPV infection and/or who test positive for an oncogenic HPV type using the clinically available HC2 test might be interested in receiving the HPV vaccine to treat their existent infection, the authors write. our results demonstrate that in women positive for HPV DNA, HPV-16/18 vaccination does not accelerate clearance of the virus and should not be used for purposes of treating prevalent infections.
In an accompanying editorial, HPV Vaccines: Prophylactic, Not Therapeutic, Lauri E. Markowitz, MD, of the Centers for Disease Control and Prevention (CDC) in Atlanta, comments on the findings of Hildesheim and colleagues.
What are the implications of these data and how do they bear on recommendations? The lack of therapeutic efficacy of the quadrivalent HPV vaccine was considered in deliberations by the Advisory Committee on Immunization Practices (ACIP). These data, along with data demonstrating the high likelihood of acquiring HPV infection soon after onset of sexual activity and data on sexual behavior in the United States, all contributed to recommendations for routine immunization at 11 to 12 years of age. Because the vaccine has no therapeutic efficacy, the greatest effect will be realized if the vaccine is administered before sexual debut, prior to exposure to HPV.
In making the recommendation for this age group, the ACIP also considered safety and immunogenicity data and programmatic issues. While there are safety and immunogenicity data in this age group through 18 months, as well as studies indicating good protection through 5 years after vaccination among older women, as for other new vaccines, data on long-term efficacy are limited. Data on longer-term efficacy will be important, particularly when targeting vaccination of 11- to 12-year-olds. Postlicensure safety monitoring, as done for all vaccines, will also be important.
Reference: JAMA. 2007;298(7):743-753 and JAMA. 2007;298(7):805-806.
Source: American Medical Association