A new study proves the HPV vaccine is even more effective than originally believed. The vaccine seems to protect against the virus on multiple sites of the body, and may even work if you are already infected, according to Time.

Daniel C. Beachler of the Infections and Immunoepidemiology Branch of the National Cancer Institute (NCI) led the study. The researchers’ methods included a randomized controlled trial, which Time terms the “gold standard of scientific research,” to test if the vaccine protected against cervical, anal and oral HPV.

Researchers followed 4,186 women, aged 18 to 25, who were either vaccinated with a HPV16/18 vaccine or a control vaccine (a hepatitis A vaccine). The women gave cervical samples at their annual visits, plus oral and anal samples at four-year follow-up visits.

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Among the women with no evidence of prior HPV exposure and infection, the vaccine was effective a whopping 83% of the time. But here’s the interesting part: it was 58% effective among women with prior HPV exposure and it was 25% effective among women with active cervical HPV16/18 infection (Time reports that this percentage was considered nonsignificant, although we are unclear what that exactly means). Overall, the vaccine efficacy was 65% for all sites and 91% for protection in at least two sites.

The U.S. Centers for Disease Control and Prevention estimates that nearly all sexually active men and women get HPV at some point in their lives.  To combat this, the CDC recommends teenagers of both sexes get the HPV vaccine  – and finish the series if they’ve started it but never finished. Women can get the vaccine through age 26, and men can get it through age 21.

Since HPV has multiple strains, it’s important to get the vaccine earlier. However, the CDC says girls who have already been sexually active can still benefit from the vaccine. It may be less effective if they were exposed to a strain not covered by the vaccine.

“My understanding was always that you get the vaccination before you get the infection and that after you’ve been infected there’s no benefit to having the vaccination,” says Dr. Miriam Longo, a head and neck cancer surgeon at Fox Chase Cancer Center who was not involved with the study, “That’s really not what the data tells us.”

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