HPV Vaccine Confers Multisite Protection

The human papillomavirus (HPV) vaccine is known to be very effective in protecting younger women who have not been exposed to HPV against cervical, anal, and oral HPV infections. Now a new study is the first to show that vaccination protects against infection at all three anatomic sites in women ages 18 to 25, including some who were previously exposed to the virus. The findings were reported at the American Association for Cancer Research Annual Meeting 2015, held in Philadelphia, PA, April 18–22.

Researchers conducted the analysis as part of the NCI-funded Costa Rica Vaccine Trial, in which 4,186 women were randomized to receive the HPV 16/18 vaccine (Cervarix; GlaxoSmithKline)—a bivalent vaccine that protects against two HPV strains that cause 70% of cervical cancers—or a control vaccine (against hepatitis A) at enrollment. In addition, participants had blood tests to detect HPV antibodies and contributed cervical samples to test for HPV DNA. Oral and anal samples were taken at a follow-up visit 4 years later.

Overall efficacy after 4 years was 65% for all sites and 91% for at least 2 of the 3 sites. Notably, the vaccine appeared to protect against concordant infections. In women diagnosed with cervical infections at follow-up, 40% in the control group had the same type of infection at oral or anal sites compared with 15% of those who received the HPV vaccine.

“Not only do we see multisite vaccine efficacy in this population, we actually see that the vaccine may provide some protection against [infection at] the other sites in previously infected women,” said Dan Beachler, PhD, MHS, cancer prevention fellow in the NCI's Division of Cancer Epidemiology and Genetics, at a press conference.

Vaccine efficacy was 84% among women with no evidence of previous exposure, 58% among those with evidence of infection prior to enrollment, and 25% among women with active infection at the time of vaccination.

The findings support current guidelines from the Centers for Disease Control and Prevention, which recommend vaccination for girls ages 11 to 12, and up to age 26 if not previously vaccinated. However, despite the availability of three vaccines that protect against infections at the different anatomic sites, only about half of U.S. females under age 18 have been vaccinated, said Beachler.

Beachler noted that the women in the study were not tested for oral or anal infections at the time of vaccination. As a result, the “naïve” group may have included women who had been exposed to HPV. If researchers had been able to identify women with evidence of anal or oral infections at enrollment, the efficacy in the naïve group could have been “closer to 100%,” he said.

“The vaccine has no therapeutic effect for women with active infections,” said Beachler. “But there are multiple HPV types that can cause cancer, and women with HPV infections could still derive protection from subsequent infections.”