Source: www.sciencenews.org Author: Nathan Seppa There are two vaccines that guard against human papilloma­virus, and they are in rare company among medical inventions — the vaccines prevent cancer. Only the hepatitis B vaccine can make the same claim. Cancer-causing HPV can trigger abnormal cell growth on the cervix, and cervical cancer still kills up to 4,000 U.S. women each year. The virus is also implicated in cancers occurring in the anus and the throat. All told, according to a 2011 study, 29 percent of sexually active U.S. girls and women carry a potentially cancer-causing HPV infection. Preteen and adolescent girls and boys are priority groups for vaccines that prevent human papillomavirus infection.© Jessica Rinaldi/Reuters/Corbis Back in 2006 and 2009, when the HPV vaccines Gardasil and Cervarix came onto the market, health officials dreamed of halting the spread of HPV, which is sexually transmitted, in a single generation. Scientists call such blanket coverage herd immunity — in which a pathogen gets vaccinated into oblivion, becoming so rare that even unvaccinated people are protected. With such heady potential, Gardasil, developed by Merck, and Cervarix, created by GlaxoSmithKline, should be an easy sell. They rev up a potent immunity against HPV 16 and 18, the two types of the virus that account for most cases of cervical cancer. Gardasil also prevents most genital warts. The immunity the vaccines provide is many-fold better than the weak protection engendered by a run-in with the virus itself, and since approval, both vaccines have proven [...]