Vaccination of women aged 18-25 with the human papillomavirus (HPV) vaccine resulted in strong protection against future infection at three anatomic sites among women without prior HPV exposure, and may still offer some protection in those with evidence of prior exposure, according to findings presented at the AACR Annual Meeting 2015, April 18-22.

“HPV is a local infection that can separately infect the cervical, anal, or oral sites where it can occasionally lead to cancer. This study demonstrates that the HPV16/18 vaccine provides protection at all three sites, particularly among women without evidence of HPV exposure prior to vaccination,” said Daniel C. Beachler, PhD, a postdoctoral fellow in the Infections and Immunoepidemiology Branch of the National Cancer Institute (NCI).

“And while the HPV vaccine is not therapeutic and cannot help clear current infections, we did observe that it may help protect some women previously exposed to HPV against subsequent infection at their noninfected sites.”

Beachler emphasised that the results of this study support current US guidelines that recommend routine vaccination for those aged 11 to 12, and vaccination through age 26 for those not vaccinated previously.

He also pointed out that this was a post-hoc analysis and that the analysis was limited to a one-time sampling of oral and anal HPV infection four years after vaccination.

“Further research and better understanding of HPV infection outside of the cervix is needed,” Beachler said.

The multisite vaccine efficacy, representing protection at all three sites, was evaluated in three subgroups.

This efficacy was 83 percent among women without evidence of prior HPV exposure, 58 percent among women with HPV exposure prior to vaccination, and a nonsignificant 25 percent among women with active cervical HPV16/18 infection at vaccination.

In all of these women combined, the overall multisite vaccine efficacy was 65 percent and increased to 91 percent for protection of at least two of the three sites.

According to Beachler, there are three HPV vaccines on the market that protect against HPV at different anatomic sites.

However, only about 50 percent of women aged younger than 18 have received the Centers for Disease Control and Prevention-recommended vaccine in the United States.

With this analysis, the researchers examined the combined effect of the HPV16/18 vaccine on multiple sites among women who were aged 18-25 at vaccination.

Beachler and colleagues conducted this analysis in the Costa Rica Vaccine Trial, a randomised, controlled trial of women who were assigned to vaccination with the HPV16/18 vaccine or a control vaccine.

Cervical samples were collected at each annual visit and oral and anal samples were collected at the four-year follow-up visit.

There were 4,186 women who contributed samples for all three sites and were included in this analysis.

Source: AACR