Another day, another study on the potentially life-saving impact of vaccines. This time it’s a new study on the vaccine against human papillomavirus, or HPV, a sexually transmitted disease that can lead to cervical cancer. Earlier this week, researchers announced that since the vaccine came on the scene, rates of HPV among young women in the U.S. have plummeted.
Published in the journal Pediatrics, the study used data from the National Health and Nutrition Examination Survey to analyze HPV prevalence among women ages 14 to 34 in the four years before the HPV vaccine was introduced in 2006 and during a four-year period after the vaccine was available. Among women, the vaccine is recommended for all young girls ages 11 to 12 and through age 26 if not previously immunized. (The vaccine is also recommended for boys, but this study focused on young girls and women.) So, here’s the big reveal: The study found that within six years of vaccine introduction, there’s been a 64 percent decrease in the prevalence of four strains of HPV among young women ages 14 to 19. Researchers also uncovered a 34 percent decrease of the four strains among women ages 20 to 24.
Study authors Lauri Markowitz, Gui Liu, Susan Hariri, Martin Steinau, Eileen Dunne and Elizabeth Unger write:
Our data confirm previous findings of an early impact of HPV vaccination in the United States among females aged 14 to 19 years and extend the findings to females in their early 20s. The decline in vaccine type prevalence after introduction of HPV vaccination is greater than expected based on current 3-dose coverage. This outcome could be due to herd protection or effectiveness of less than a complete 3-dose series, for which there is accumulating evidence.
Digging deeper into the study’s findings, researchers found that the greatest decline in the four strains of HPV — these are the four strains covered by the quadrivalent HPV vaccine, also referred to as 4vHPV — were observed among young women ages 14 to 19. This age group also has the highest HPV vaccination rate. The study reported that just 51 percent of those ages 14 to 19 received at least one dose of HPV vaccine (full vaccination is three doses). But that somewhat-suboptimal vaccine coverage percentage, coupled with news of a 64 percent drop in HPV prevalence, seems to reflect just how effective the vaccine is.
The study did not find a decrease in HPV prevalence among women ages 24 to 29 and 30 to 34. Also, researchers couldn’t find evidence of herd immunity effects in this study; however, they noted that herd effects have been observed for genital warts and HPV in countries with higher HPV vaccination rates.
According to the Centers for Disease Control and Prevention, about 79 million Americans are currently infected with HPV and 14 million new cases occur each year. The nation’s most common sexually transmitted disease, HPV often goes away on its. But when it doesn’t, it can cause genital warts and cervical cancer, as well as cancers of the vulva, anus, vagina and penis. Two strains of HPV — both of which are covered in the vaccine — cause 70 percent of cervical cancers worldwide. CDC reports that four out of 10 girls remain unvaccinated against HPV, as do six out of 10 boys.
For a copy of the new HPV study, visit Pediatrics.
Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for nearly 15 years.